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PABA (Para-Aminobenzoic Acid): Uses, Evidence, and Safety

Overview

Plain-English information for everyday use

1. What Is PABA?

Key Takeaway

PABA was once called "vitamin B10," but it is not actually a vitamin for humans. It's a compound that bacteria use to make folate — which is also why sulfa antibiotics work.

PABA (para-aminobenzoic acid) is a small compound that was historically labeled "vitamin B10" or "vitamin Bx." That label is misleading: PABA is not an essential vitamin for humans. Bacteria, plants, and fungi use PABA as a building block to make folate (vitamin B9), but the human body doesn't make folate this way — we get folate from food. So there is no such thing as a human PABA deficiency. Krátký M, et al. 4-Aminobenzoic Acid Derivatives. Open Source ↗

This bacterial role is actually why sulfa antibiotics work — they block the bacterial enzyme that uses PABA, starving bacteria of folate. (It's also why taking PABA can interfere with those antibiotics — see Section 3.) Engevik MA, et al. Microbial Folate Synthesis. Open Source ↗

Two things to keep separate. The PABA sold as a supplement is the plain acid. A different, prescription-only form — potassium aminobenzoate (brand name Potaba) — is a medicine used for certain scar-tissue conditions. They aren't interchangeable, and this page is about the supplement. Weidner W, et al. Eur Urol. 2005. Open Source ↗

Key Highlights

Not a real vitamin for humans, despite the old "vitamin B10" name
A folate building block for bacteria — the reason sulfa antibiotics work
No human deficiency state exists, so there's nothing to "correct"
Its popular supplement uses (gray hair, skin pigment, energy) are old and unproven (Section 6)
Important: high doses have caused rare liver injury and strong allergic reactions (Section 5)
Was once a sunscreen ingredient, but was removed over allergy and skin-reaction concerns

2. Why People Take It

Key Takeaway

PABA is marketed mostly for reversing gray hair and as a vague "anti-aging" nutrient. The evidence behind these claims is old, uncontrolled, and doesn't hold up — and because PABA isn't a vitamin, there's no deficiency to fix.

Here's an honest look at the reasons people reach for PABA, and what the evidence actually shows: Zarafonetis CJD. Gray-hair darkening during para-aminobenzoic acid therapy. 1950. Open Source ↗

Reversing gray hair — the best-known claim, but it rests on uncontrolled reports from the 1940s–50s, and any darkening fades once you stop.
Skin-pigment conditions — promoted historically, but supported only by anecdotes.
Energy, "anti-aging," or as a "B-complex vitamin" — PABA isn't an essential nutrient, so the "vitamin" rationale doesn't apply.

A reality check: low energy or graying hair are not specific — they have many different causes, and PABA is not a vitamin you can be deficient in. It is a dietary supplement, not a remedy for any specific health problem, and it is not a substitute for the prescription medicine. Given the lack of proven benefit and the real safety concerns below, there is little reason to take PABA. Talk to your healthcare provider before starting it — especially if you take any antibiotics.

3. Who Should Be Careful

Key Takeaway

Never take PABA with sulfa antibiotics — it can make them stop working. Avoid it if you're allergic to PABA or related compounds (some anesthetics, hair dyes, sulfa drugs), and be cautious with any liver concerns.

Do not use PABA — or talk with your healthcare provider first — if you:

Take a sulfa antibiotic (such as sulfamethoxazole). PABA can block these antibiotics and reduce their effectiveness, so the two should not be combined. The same applies to dapsone and a few other related medicines. Krátký M, et al. 4-Aminobenzoic Acid Derivatives. Open Source ↗
Are allergic to PABA or "para-group" compounds — including ester-type numbing agents (benzocaine, procaine), permanent hair dyes, and sulfa drugs. These can cross-react. European Medicines Agency. Potassium para-aminobenzoate — CMDh Scientific Conclusions. Open Source ↗
Have any liver condition. High-dose PABA has caused rare liver injury, so people with liver problems should avoid it. Roy J, Carrier S. Acute liver injury with potassium para-aminobenzoate. J Sex Med. 2008. Open Source ↗
Are prone to low blood sugar. PABA can cause low blood sugar, especially if taken while fasting — take it with food, and be cautious if you have a blood-sugar condition. European Medicines Agency. Potassium para-aminobenzoate — CMDh Scientific Conclusions. Open Source ↗
Have reduced kidney function. PABA is cleared by the kidneys, so clearance is slower and dosing less certain. Meyer B, Gyr K. Oral NBT-PABA pancreatic function test. 1987. Open Source ↗

If You're Pregnant or Breastfeeding

P-3 — Insufficient data (precautionary) Breast-milk transfer: T-U (unstudied)

The safety of PABA supplements in pregnancy has not been established, and there's no proven benefit to weigh against the unknowns — so avoid supplemental PABA in pregnancy unless a doctor specifically recommends it. European Medicines Agency. Potassium para-aminobenzoate — CMDh Scientific Conclusions. Open Source ↗

For breastfeeding, it isn't known whether PABA passes into breast milk or how it might affect a nursing infant. Discuss it with a lactation consultant or your pediatrician, and you can ask them to check the LactMed database. Centers for Disease Control and Prevention. Breastfeeding & Medications. Open Source ↗

Stop and Seek Medical Attention If:

You notice signs of liver trouble — yellowing of the skin or eyes, dark urine, pale stools, belly pain, or marked fatigue.
You develop a rash with fever, or facial/throat swelling or trouble breathing (a severe allergic reaction) — get emergency care.
You feel shaky, sweaty, or faint from low blood sugar.
These reactions are most likely in the first couple of months of use.

4. Using It Sensibly

Key Takeaway

Because there's no proven benefit and real risks, the most sensible approach for most people is to skip PABA. If you do use it, keep doses low, take it with food, and watch for warning signs early on.

Practical Tips

Consider whether you need it at all. PABA isn't a vitamin, and its supplement claims aren't supported — so for most people there's little reason to take it.
Check your medicines first. If you take a sulfa antibiotic (or dapsone), don't use PABA. Krátký M, et al. 4-Aminobenzoic Acid Derivatives. Open Source ↗
Keep doses modest and take with food. Food reduces stomach upset and helps prevent low blood sugar. European Medicines Agency. Potassium para-aminobenzoate — CMDh Scientific Conclusions. Open Source ↗
Watch the first two months. That's when allergic reactions and liver injury are most likely — report a rash, fever, or yellowing promptly. European Medicines Agency. Potassium para-aminobenzoate — CMDh Scientific Conclusions. Open Source ↗
Don't use it as a stand-in for prescribed care. The prescription form is a different product used under medical supervision.

5. Side Effects

Key Takeaway

Most side effects are stomach upset or skin reactions, but the serious ones to know about are rare liver injury and strong allergic reactions — most likely in the first couple of months.

Most reported problems come from the higher-dose prescription form, but supplement doses still carry some risk: European Medicines Agency. Potassium para-aminobenzoate — CMDh Scientific Conclusions. Open Source ↗

Stomach upset — nausea, loss of appetite, or cramping; the most common complaint and the main reason people stop.
Allergic skin reactions — rash, welts, or itching; PABA is a known skin sensitizer.
Rare but serious: liver injury. High-dose use has caused acute liver injury, usually with an allergic flavor (rash and fever), and it clears when the supplement is stopped. Roy J, Carrier S. Acute liver injury with potassium para-aminobenzoate. J Sex Med. 2008. Open Source ↗ Al Attar L, Kilgore W. Acute liver injury with potassium aminobenzoate. 2018. Open Source ↗
Low blood sugar — especially if taken while fasting.
Gradual darkening of gray hair or skin pigment — a recognized effect at higher doses.

One more point on sunscreen. PABA used to be a sunscreen ingredient, but it was removed because of allergic and light-triggered skin reactions; US regulators no longer recognize it as a safe-and-effective sunscreen ingredient. U.S. Food and Drug Administration. Sunscreen Drug Products — Proposed Order (OTC000008). Open Source ↗

6. What Research Suggests

Key Takeaway

The supplement claims don't hold up under scrutiny, and even the prescription form barely outperforms placebo for the conditions it's used for.

Gray hair — old and unconvincing. Reports from the 1940s–50s described hair re-darkening at high doses, and hair darkening is a recognized PABA effect. But these studies were uncontrolled, the effect fades when you stop, and no modern controlled trial supports it. Zarafonetis CJD. Gray-hair darkening during para-aminobenzoic acid therapy. 1950. Open Source ↗

The "vitamin B10" claims — not established. A cluster of mid-century claims tied PABA to low energy, "tired blood," low mood, skin rashes, fertility, and joint complaints. These rest on uncontrolled historical reports, and because PABA isn't an essential nutrient, the idea of correcting a "deficiency" doesn't apply. Engevik MA, et al. Microbial Folate Synthesis. Open Source ↗

The prescription form, for the record. The prescription salt (Potaba) is used for scar-tissue conditions. In the best trial — for a condition that causes curvature of the penis (Peyronie's disease) — it shrank the scar plaque and slowed progression but did not improve curvature or pain; broader reviews find no oral therapy reliably beats placebo, and the leading urology guideline does not recommend it. Weidner W, et al. Eur Urol. 2005. Open Source ↗ Peyronie Disease. StatPearls (NCBI Bookshelf). Open Source ↗

A telling negative. For a condition that hardens the skin and connective tissue, a rigorous controlled trial found the prescription form ineffective — a useful illustration that long use and old enthusiasm don't equal proven benefit. Clegg DO, et al. Randomized placebo-controlled trial, 1994. Open Source ↗

7. Food Sources

Key Takeaway

PABA turns up in small amounts in foods like liver, yeast, and whole grains. There's no recommended intake because it isn't an essential nutrient.

Food source	Notes
Liver and organ meats	Among the richer dietary sources
Brewer’s yeast	Traditional source
Whole grains	Small amounts
Eggs	Small amounts

PABA is found in small amounts in a range of foods — liver and kidney, brewer's and baker's yeast, molasses, mushrooms, whole grains, wheat germ and bran, spinach, and eggs. Even the richer sources provide only modest amounts. PubChem (NIH). Compound Summary: 4-Aminobenzoic acid (CID 978). Open Source ↗

Because PABA is not an essential nutrient, there is no recommended daily intake and no deficiency to avoid — a normal varied diet provides whatever small amounts the body encounters. Engevik MA, et al. Microbial Folate Synthesis. Open Source ↗

8. What It Does in the Body

Key Takeaway

In humans, PABA has no vitamin role — it's absorbed, processed, and quickly passed in the urine. That quick, predictable handling is actually why it's used as a lab marker.

Unlike a true vitamin, PABA has no essential job in the human body. What it does do is straightforward:

In bacteria (not in you), it's a building block for folate. Krátký M, et al. 4-Aminobenzoic Acid Derivatives. Open Source ↗
In your body, it's absorbed quickly, processed by the liver, and passed out in the urine within hours. Meyer B, Gyr K. Oral NBT-PABA pancreatic function test. 1987. Open Source ↗
The prescription form is thought to act on scar tissue, but exactly how is uncertain. Peyronie Disease. StatPearls (NCBI Bookshelf). Open Source ↗

These are general, structure-and-function points — these are not medical claims about these systems.

9. Frequently Asked Questions

Is PABA a vitamin (vitamin B10)?

No. The "vitamin B10" name is an old misnomer. PABA is a folate building block for bacteria, but humans don't make folate that way, so it isn't an essential vitamin and there's no human deficiency. Krátký M, et al. 4-Aminobenzoic Acid Derivatives. Open Source ↗

Will PABA reverse my gray hair?

The evidence doesn't support it. Old, uncontrolled reports described darkening at high doses, but the effect fades when you stop and no modern controlled trial backs it up. Zarafonetis CJD. Gray-hair darkening during para-aminobenzoic acid therapy. 1950. Open Source ↗

Is the supplement the same as the prescription Potaba?

No. The supplement is plain PABA; Potaba is a prescription potassium salt used at much higher doses under medical supervision for scar-tissue conditions. They aren't interchangeable. U.S. Food and Drug Administration. Drug Efficacy Study Implementation: Potassium Aminobenzoate. Federal Register. Open Source ↗

Can I take PABA with my antibiotics?

Not with sulfa antibiotics (or dapsone). PABA can block how these drugs work and reduce their effectiveness, so they shouldn't be combined. Krátký M, et al. 4-Aminobenzoic Acid Derivatives. Open Source ↗

Isn't PABA a sunscreen?

It used to be. PABA absorbs UV light, but it was removed from sunscreens because of allergic and light-triggered skin reactions, and US regulators no longer recognize it as a safe-and-effective sunscreen ingredient. U.S. Food and Drug Administration. Sunscreen Drug Products — Proposed Order (OTC000008). Open Source ↗

Can PABA hurt my liver?

Rarely, yes — high-dose use has caused acute liver injury, usually with an allergic pattern, in the first couple of months. It clears on stopping, but it's a real reason to avoid high doses and to skip PABA if you have liver problems. Roy J, Carrier S. Acute liver injury with potassium para-aminobenzoate. J Sex Med. 2008. Open Source ↗

Do I actually need PABA?

No — it isn't an essential nutrient, so you can't be deficient in it, and its supplement claims aren't supported. For most people there's no reason to take it. Engevik MA, et al. Microbial Folate Synthesis. Open Source ↗

10. Choosing a Quality Product

Key Takeaway

The bigger question is whether to take PABA at all. If you do, choose a third-party-tested product, keep the dose low, and read the label carefully.

Before thinking about product quality, weigh whether PABA is worth taking given the lack of proven benefit and the safety concerns above. If you still choose to use it, the basics apply: PubChem (NIH). Compound Summary: 4-Aminobenzoic acid (CID 978). Open Source ↗

What to Look For

Clear labeling: "PABA" or "para-aminobenzoic acid" and the amount per serving
Third-party testing: USP, NSF, or an equivalent quality seal
A modest dose: lower is safer; high doses carry the most risk
Honest claims: be skeptical of products promising to reverse gray hair or "boost energy"
Not the prescription form: the supplement is plain PABA, not potassium aminobenzoate (Potaba)

11. Genes & How You Process PABA

Key Takeaway

Your body clears PABA using "acetylator" enzymes that vary from person to person — the same gene family that affects how people handle certain medications.

After you absorb PABA, your body attaches small chemical tags to it (a process called acetylation) before clearing it in the urine. The enzymes that do this — the NAT acetyltransferases — vary genetically, so people are "fast" or "slow" acetylators, the same trait that affects how some medicines are processed. Meyer B, Gyr K. Oral NBT-PABA pancreatic function test. 1987. Open Source ↗

The other "genetics" worth knowing is bacterial, not human: bacteria carry the enzyme that turns PABA into folate, which humans lack — the basis for both PABA's non-vitamin status and the way sulfa antibiotics work. Krátký M, et al. 4-Aminobenzoic Acid Derivatives. Open Source ↗

12. Where PABA Comes From

Key Takeaway

PABA isn't a traditional herbal remedy — it's a 20th-century laboratory compound that got mislabeled as a "vitamin," then found uses as a sunscreen and a prescription drug.

PABA has no folk-medicine history. It's a defined chemical that was identified in the early 20th century as part of the folate molecule, which led to its (incorrect) labeling as a "vitamin." From there it had a run as a sunscreen ingredient and as the basis of a prescription medicine, before being reassessed as the evidence matured. PubChem (NIH). Compound Summary: 4-Aminobenzoic acid (CID 978). Open Source ↗

13. Story Behind the Science

Key Takeaway

PABA's story is a cautionary one: a mid-century "vitamin" and gray-hair cure, then a sunscreen, then a niche drug — with each wave of enthusiasm outrunning the evidence.

In the 1940s–50s PABA was promoted as "vitamin B10" and as a gray-hair remedy, and it became a popular sunscreen ingredient. Over the following decades, the picture changed: it was recognized as not being a human vitamin, and it was removed from sunscreens over allergy and skin-reaction concerns. U.S. Food and Drug Administration. Sunscreen Drug Products — Proposed Order (OTC000008). Open Source ↗

The prescription salt found a niche for scar-tissue conditions, but modern trials and reviews have been underwhelming, and regulators classify its uses as only "possibly effective" — a reminder that a long history of use is not the same as proof. U.S. Food and Drug Administration. Drug Efficacy Study Implementation: Potassium Aminobenzoate. Federal Register. Open Source ↗

14. Lab Tests

Key Takeaway

PABA is itself used as a lab marker, so taking it as a supplement can throw off certain urine and digestion tests. Tell your provider if you take it.

Here's an unusual quirk: PABA is used as a laboratory marker — to check whether a 24-hour urine collection is complete, and in an older test of how well the pancreas is working. If you take PABA supplements, you can throw off these tests, and PABA can also interfere with certain lab color-based assays. So tell your provider and the lab if you use it. Meyer B, Gyr K. Oral NBT-PABA pancreatic function test. 1987. Open Source ↗

If you develop any symptoms that could suggest liver trouble while taking PABA, your provider may check liver blood tests — the first couple of months carry the highest risk. European Medicines Agency. Potassium para-aminobenzoate — CMDh Scientific Conclusions. Open Source ↗

✓ Last Reviewed: June 2026

PABA (Para-Aminobenzoic Acid)

Technical Data

Clinical reference for healthcare professionals

CLINICAL SUMMARY

PABA (Para-Aminobenzoic Acid)

PABA (4-aminobenzoic acid; PubChem CID 978) — an aromatic amine and the microbial substrate for dihydropteroate synthase in folate biosynthesis, historically mislabeled "vitamin B10." It is not a human vitamin (humans lack the folate-synthesis pathway; there is no deficiency state). A separate prescription drug, potassium aminobenzoate (Potaba), is used for scar-tissue (fibrosing) conditions on weak evidence. Key interaction: PABA antagonizes sulfonamide antibacterials (a absolute restriction).

Overall Evidence (supplement)

Insufficient

Primary Uses Studied

InsufficientPremature gray hair (supplement) · old, uncontrolled reports; relapses on discontinuation
InsufficientSkin-pigment conditions (supplement) · anecdotal only; unproven
Insufficient"Vitamin B10" claims (energy, mood, etc.) · historical; not a nutrient, no deficiency
LimitedPeyronie's disease (Potaba, DRUG) · plaque/progression effect, NO curvature/pain benefit
InsufficientSkin-hardening condition (Potaba, DRUG) · controlled RCT negative

Standard Intake Range

Supplement (free PABA): ~100–500 mg/day — no established basis; not a nutrient (no requirement)
Take with food to reduce GI upset and prevent low blood sugar
Prescription DRUG (Potaba): 12 g/day in divided doses with food, under specialist care — context only, not a supplement dose

Key Safety Flags

🟢 RAPIDLY CLEARED renally; no dependence or withdrawal — can be stopped abruptly
🟠 CAUTION Rare immunoallergic liver injury (EMA-recognized), usually within ~8 weeks; reversible on stopping
🟠 CAUTION Strong sensitizer — allergic/light-triggered skin reactions; broad para-group cross-reactivity
🟠 CAUTION Dose-limiting GI intolerance (leading cause of discontinuation)
🟠 CAUTION Fasting low blood sugar — take with food; caution in blood-sugar conditions
🔴 DO NOT USE With sulfonamide antibacterials (antagonism); in PABA/para-group allergy; or after prior PABA-induced liver injury or severe allergic reaction

Monitoring Quick-Ref

Liver blood tests: if symptoms arise, especially in the first ~8 weeks
Blood glucose: in at-risk users (fasting low blood sugar)
Lab-test awareness: PABA confounds urine-completeness and pancreatic-function tests

⚠️ Lab Interference

PABA is itself a diagnostic marker. Supplement use confounds the 24-hour-urine-collection-completeness marker and the NBT-PABA / bentiromide indirect pancreatic-function test, and PABA's arylamine chemistry interferes with certain colorimetric assays. Record PABA use on requisitions for these tests and for amino-acid/organic-acid panels.

Clinical bottom line: PABA is not a human vitamin (microbial folate substrate; no deficiency state); the "vitamin B10" supplement claims (gray hair, skin pigment, energy) are old, uncontrolled, and unsupported. The separate prescription form (potassium aminobenzoate, Potaba) for scar-tissue conditions barely outperforms placebo (best Peyronie's RCT: plaque/progression effect, no curvature/pain benefit; a controlled trial in a skin-hardening condition was negative; FDA rates indications only "possibly effective"). Real risks include rare immunoallergic liver injury and severe allergic reactions (usually within ~8 weeks), dose-limiting GI intolerance, fasting low blood sugar, and broad para-group cross-reactivity. Must not be used with sulfonamide antibacterials. Removed from sunscreens (FDA not-GRASE). Pregnancy/lactation: P-3 / T-U. For most people there is no clinical reason to use it.

1. Identity & Forms

Key Takeaway

PABA (4-aminobenzoic acid; CID 978, CAS 150-13-0; C₇H₇NO₂) is an aromatic amine, not a vitamin. Subject form = free PABA (supplement). Distinct from potassium aminobenzoate (Potaba, the Rx salt) and from the PABA-ester anesthetics.

Common name	PABA (para-aminobenzoic acid)
Synonyms	4-aminobenzoic acid; historically "vitamin B10" / "vitamin Bx" (not a recognized vitamin)
IUPAC name	4-aminobenzoic acid
CAS Registry	150-13-0
Molecular formula	C₇H₇NO₂
Molecular weight	137.14 g·mol⁻¹
PubChem CID	978
Chemical class	Aromatic amine (not a vitamin)
Subject form	Free PABA (dietary supplement)
Related prescription salt	Potassium aminobenzoate (Potaba) — distinct Rx agent
Appearance	White to off-white crystalline powder

Identity. PABA — para-aminobenzoic acid / 4-aminobenzoic acid — is a benzene ring bearing an amino group para to a carboxyl group: an aromatic amine and non-proteinogenic amino acid (C₇H₇NO₂; MW 137.14; CAS 150-13-0; CID 978; DrugBank DB02362). Obsolete names: vitamin Bx, vitamin B10, vitamin H1. White-to-grey crystalline solid, mp 187–189 °C, slightly water-soluble. PubChem (NIH). Compound Summary: 4-Aminobenzoic acid (CID 978). Open Source ↗

Forms. Free PABA (subject) is the supplement form and the urinary/pharmacokinetic marker reagent. Potassium aminobenzoate (Potaba) is the prescription potassium salt (500 mg capsules) used for fibrosing conditions — scar-tissue conditions including skin-hardening conditions, dermatomyositis, morphea, pemphigus, and Peyronie's disease. Sodium PABA is historical. PABA is also the parent of the ester-type "caine" local anesthetics (procaine, benzocaine) and the discontinued sunscreen ester padimate-O — relevant to allergic cross-sensitivity. Weidner W, et al. Eur Urol. 2005. Open Source ↗

2. Mechanism of Action

Key Takeaway

PABA is the microbial substrate for dihydropteroate synthase (folate synthesis); humans lack this pathway — the basis for both its non-vitamin status and sulfonamide selectivity (and antagonism). The prescription form's antifibrotic mechanism is uncertain.

Microbial folate synthesis & sulfonamide relationship. PABA is the obligate substrate of dihydropteroate synthase (DHPS; gene folP): DHPS condenses PABA with a dihydropterin to form dihydropteroate, converted onward to tetrahydrofolate. This pathway operates in bacteria, plants, and fungi but not in humans — which is why PABA is not a human vitamin and why this step underlies the selective toxicity of sulfonamide antibacterials (structural PABA analogs that competitively occupy the DHPS site). Conversely, supplemental PABA competitively antagonizes sulfonamides and can reduce their efficacy (a formal restriction). Krátký M, et al. 4-Aminobenzoic Acid Derivatives. Open Source ↗ Engevik MA, et al. Microbial Folate Synthesis. Open Source ↗

Antifibrotic mechanism (Potaba) — proposed, not established. The prescription salt is used as an antifibrotic/anti-inflammatory agent, but its mechanism is genuinely uncertain (FDA classifies the indications "possibly effective"). Hypotheses include increasing tissue oxygen uptake — which, because monoamine oxidase requires oxygen, may enhance MAO activity and lower local serotonin (implicated in fibrogenesis) — plus inhibition of fibroblast glycosaminoglycan secretion and reduced collagen formation. PABA also has in-vitro antioxidant activity and absorbs UVB (the basis of its former sunscreen use). Peyronie Disease. StatPearls (NCBI Bookshelf). Open Source ↗

3. Pharmacokinetics (ADME)

Key Takeaway

Rapid, near-complete absorption; Phase II conjugation (N-acetylation by NAT1 + glycine conjugation by GLYAT), saturating near 800 mg; rapid renal clearance (>90% in ~8 h), reduced in renal impairment and the elderly. These properties underpin its diagnostic-marker uses.

Absorption & metabolism. PABA is rapidly and nearly completely absorbed (in-situ perfusion ~100%; oral urinary recovery >85%). It undergoes Phase II conjugation — N-acetylation by arylamine N-acetyltransferase 1 (NAT1) to N-acetyl-PABA, and glycine conjugation by glycine N-acyltransferase (GLYAT) to p-aminohippuric acid — plus minor glucuronidation; very little free PABA is excreted. At high oral doses (~800 mg) acetylation/glucuronidation saturate, shifting metabolite ratios. Meyer B, Gyr K. Oral NBT-PABA pancreatic function test. 1987. Open Source ↗

Excretion & diagnostic use. Elimination is renal and rapid — >90% of an oral dose recovered within ~8 h; recovery is reduced in renal impairment and in the elderly (delayed clearance). This complete absorption plus quantitative renal excretion underpins PABA's use as a 24-hour-urine-completeness marker and the NBT-PABA (bentiromide) indirect pancreatic-exocrine-function test (oral bentiromide is cleaved by chymotrypsin to release PABA, which is absorbed, conjugated, and renally excreted). Meyer B, Gyr K. Oral NBT-PABA pancreatic function test. 1987. Open Source ↗

4. Organ System Effects

Key Takeaway

The clinically meaningful effects are hepatic (rare immunoallergic liver injury, with a no-causal-harm counterpoint), dermatologic/immune (strong sensitizer; cross-reactivity; hyperpigmentation), metabolic (fasting low blood sugar), and GI (dose-limiting). Renal is the elimination route.

System	Effect	Notes
Hepatic	Rare immunoallergic liver injury	Mostly with the multi-gram Rx form; reversible on stopping
Dermatologic / immune	Strong skin sensitizer; cross-reactivity; skin darkening	Basis of historical sunscreen use and contact skin rash
Metabolic	Fasting low blood sugar	Reported at higher doses; take with food
Gastrointestinal	Nausea, dose-limiting stomach upset	Most common reason for stopping
Renal	Primary elimination route	Excreted in urine, largely as conjugates

Hepatic & immune/skin. The principal serious effect is rare idiosyncratic, immune-pattern liver injury (EMA-recognized) — typically with onset within ~8 weeks, often accompanied by rash, fever, and eosinophilia, and reversible on discontinuation; a large retrospective series in a skin-hardening condition found no causal hepatotoxicity (a balanced counterpoint). Dermatologically, PABA is a strong sensitizer causing allergic and light-triggered skin reactions with broad para-group cross-reactivity, plus gradual hair/skin hyperpigmentation at higher doses. European Medicines Agency. Potassium para-aminobenzoate — CMDh Scientific Conclusions. Open Source ↗ Zarafonetis CJ, et al. Hepatic findings with potassium para-aminobenzoate. 1986. Open Source ↗

Metabolic, GI & renal. Metabolic: fasting low blood sugar (impaired gluconeogenesis), preventable with food. GI: dose-limiting nausea/anorexia/cramping at multi-gram doses (the leading cause of discontinuation). Renal: the elimination route; clearance is delayed in renal impairment, and the potassium salt adds a potassium load relevant in renal impairment. European Medicines Agency. Potassium para-aminobenzoate — CMDh Scientific Conclusions. Open Source ↗

5. Dosing (Supplement vs Drug)

Key Takeaway

Supplement free PABA is taken at ~100–500 mg/day with no established basis (PABA is not a nutrient). The prescription drug (Potaba) is dosed far higher (12 g/day, divided, with food) under supervision — context only. Always take with food.

Context	Form	Typical amount	Notes
Supplement	Free PABA	~100–500 mg/day	No established nutritional basis (not a nutrient); take with food
Prescription (context only)	Potassium aminobenzoate (Potaba)	~12 g/day, divided, with food	Physician-supervised; not a supplement dose

5A. Supplement Dosing

Free PABA: ~100–500 mg/day in marketed products — no established efficacy basis; PABA is not a nutrient, so there is no requirement.
Take with food to reduce GI upset and prevent fasting low blood sugar; stop during fasting/illness. European Medicines Agency. Potassium para-aminobenzoate — CMDh Scientific Conclusions. Open Source ↗

5B. Prescription Drug Dosing (context only)

Potassium aminobenzoate (Potaba): 12 g/day in divided doses (e.g., 500 mg capsules), taken with food; pediatric dosing is weight-based under medical supervision. Weidner W, et al. Eur Urol. 2005. Open Source ↗
Stop-use: discontinue immediately and do not re-challenge for liver-injury or hypersensitivity signs; interrupt for anorexia/nausea; no taper needed (rapidly cleared). Roy J, Carrier S. Acute liver injury with potassium para-aminobenzoate. J Sex Med. 2008. Open Source ↗

This drug dosing is provided to distinguish supervised medical use from supplementation — it is not guidance for supplement users.

6. Clinical Evidence

Key Takeaway

Supplement claims (gray hair, pigment, "vitamin B10") are Insufficient. The prescription Peyronie's use is Limited (plaque effect, no curvature/pain); the skin-hardening-condition RCT was negative. By contrast, PABA's microbial-folate role and its lab-marker use rest on Strong data, and its pharmacokinetics are Moderately well-characterized.

Supplement claims — Insufficient. Premature gray-hair re-darkening rests on uncontrolled 1940s–50s reports and relapses on discontinuation; skin-pigment and "vitamin B10" claims (energy, mood, joint complaints) are historical and unsupported, and PABA's non-nutrient status removes any deficiency rationale. Zarafonetis CJD. Gray-hair darkening during para-aminobenzoic acid therapy. 1950. Open Source ↗

Prescription Peyronie's use — Limited. The only modern randomized, placebo-controlled trial (Weidner 2005; 103 men, 12 months) showed a significant plaque effect and prevented curvature progression, but no improvement in pre-existing curvature and no effect on pain; broader systematic and network analyses find no oral monotherapy reliably beats placebo, and the AUA does not recommend it (no oral option carries a grade-A recommendation). Weidner W, et al. Eur Urol. 2005. Open Source ↗ Park TY, et al. Medical management of Peyronie's disease — systematic review. 2016. Open Source ↗

Skin-hardening condition — negative (decisive). A 48-week randomized, double-blind, placebo-controlled trial of the prescription salt (12 g/day) was ineffective for the skin condition — controlled evidence does not support it. Clegg DO, et al. Randomized placebo-controlled trial, 1994. Open Source ↗

Well-established by contrast. What is supported by Strong, consistent data is PABA's biochemical role as a microbial folate substrate and its validated use as a urinary/pancreatic-function lab marker; its rapid, near-complete pharmacokinetics are Moderately well-characterized. None of this confers a supplement benefit. Krátký M, et al. 4-Aminobenzoic Acid Derivatives. Open Source ↗

7. Pharmacogenomics & Genetics

Key Takeaway

PABA clearance depends on NAT acetyltransferases, which vary genetically (fast vs slow acetylators). The defining "genetics," though, is microbial: bacteria carry the DHPS folate pathway that humans lack.

PABA's Phase II handling depends on arylamine N-acetyltransferases (NAT1/NAT2), whose genetic polymorphisms produce the well-known fast/slow acetylator phenotypes that also modulate the metabolism of several drugs — a source of inter-individual variability in PABA conjugation. The more fundamental genetic distinction is between humans (who lack the DHPS folate-synthesis pathway, hence PABA's non-vitamin status) and the bacteria/plants/fungi that possess it (the basis of sulfonamide selectivity and of PABA's antagonism of those antibacterials). Krátký M, et al. 4-Aminobenzoic Acid Derivatives. Open Source ↗

8. Adverse Effects

Key Takeaway

Most events are GI or hypersensitivity-related. The serious ones — rare immunoallergic liver injury and severe allergic reactions — cluster in the first ~8 weeks and are reversible on stopping. Most data are from the multi-gram prescription form; supplement doses carry lower but non-zero risk.

Effect	Approx. frequency	Notes
Nausea / stomach upset	Common	Dose-related; take with food
Skin rash / sensitization	Uncommon	PABA is a known contact sensitizer
Low appetite, fatigue	Uncommon	Usually at higher doses
Fasting low blood sugar	Rare	Higher doses; mitigated by taking with food
Immunoallergic liver injury	Rare	Clusters in the first ~8 weeks; reversible on stopping
Severe allergic reaction	Rare	Stop and seek care

Profile by system. Skin/immune: allergic and light-triggered skin reactions (PABA is a strong sensitizer; historically the most common sunscreen photoallergen), welts, itching, rare severe allergic reaction (facial/throat swelling, breathing difficulty), and a severe whole-body drug-allergy reaction (rash + fever + eosinophilia + organ involvement); broad para-group cross-reactivity (sulfonamides, ester anesthetics, hair dyes, thiazides). Hepatobiliary: rare immunoallergic liver injury (EMA-recognized; <8-week onset; reversible) — with a retrospective counterpoint finding no causal hepatotoxicity. Metabolic: fasting low blood sugar. GI: dose-limiting nausea/anorexia (leading cause of discontinuation). Skin pigment: gradual hair/skin hyperpigmentation. European Medicines Agency. Potassium para-aminobenzoate — CMDh Scientific Conclusions. Open Source ↗

Dose context & sunscreen note. Most labeled events derive from the prescription multi-gram range; consumer free-PABA doses (~100–500 mg) carry lower but non-zero risk. Separately, PABA's allergic/light-triggered skin reactions and its potential to add to UV-related skin damage were the basis for its removal from sunscreens (FDA not-GRASE). U.S. Food and Drug Administration. Sunscreen Drug Products — Proposed Order (OTC000008). Open Source ↗

9. Drug Interactions

Key Takeaway

The major interaction is antagonism of sulfonamide antibacterials (must not be used), with the same applying to dapsone and PAS. Also: reduced tetracycline absorption, additive low blood sugar with antidiabetics, increased corticosteroid exposure, and broad para-group allergic cross-reactivity.

9A. By Mechanism

Antibacterials. Sulfonamides (sulfamethoxazole, sulfadiazine, sulfasalazine): MAJOR — PABA competitively antagonizes them at DHPS, reducing efficacy; must not be used concurrently. The same antifolate antagonism applies to dapsone and para-aminosalicylic acid (PAS). Tetracyclines: the potassium salt impairs oral absorption — separate dosing. Krátký M, et al. 4-Aminobenzoic Acid Derivatives. Open Source ↗

Other agents & anti-doping. Antidiabetics/insulin: additive low blood sugar (and sulfonylureas are para-group — cross-sensitivity) — monitor glucose. Corticosteroids: PABA may slow their breakdown, increasing exposure. Ester anesthetics, paraphenylenediamine hair dyes, azo dyes, thiazides: para-group allergic cross-reactivity. Beta-blockers: may mask low-blood-sugar symptoms. Alcohol/other hepatotoxins: theoretical additive liver risk. PABA is not on the WADA Prohibited List and is not performance-enhancing (strict-liability/contamination caveats apply). European Medicines Agency. Potassium para-aminobenzoate — CMDh Scientific Conclusions. Open Source ↗

9B. Herb–Drug Interaction & Drug-Nutrient Depletion Table

PABA is not a nutrient depleter; the table summarizes the clinically relevant interactions, the most important being sulfonamide antagonism.

Agent / class	Interaction & evidence	Action
Sulfonamide antibacterials	Competitive antagonism at DHPS — reduced efficacy	Must not be used — do not combine
Dapsone; para-aminosalicylic acid	Same antifolate antagonism	Avoid / monitor
Tetracyclines	Potassium salt impairs oral absorption	Separate dosing
Antidiabetics / insulin	Additive low blood sugar; sulfonylureas para-group	Monitor glucose
Corticosteroids	PABA may slow corticosteroid breakdown	Monitor for increased effect
Ester anesthetics; hair dyes; thiazides	Para-group allergic cross-reactivity	Caution in para-group allergy
Dietary nutrients	No depletion caused by PABA	PABA is not a depleter

10. Cautions and Considerations

Key Takeaway

Absolute restrictions: concurrent sulfonamides, PABA/para-group allergy, and prior PABA-induced liver injury or severe allergy. Relative cautions: renal impairment, active liver disease, and blood-sugar-prone individuals. Pregnancy/lactation: P-3 / T-U.

10A. Restrictions by Population

Concurrent sulfonamide antibacterials: must not be used (antagonism). Avoid in anyone needing sulfonamides, dapsone, or PAS.
PABA / para-group allergy: must not be used (cross-reactivity with ester anesthetics, hair dyes, sulfa drugs, thiazides).
Prior PABA-induced liver injury or severe allergic reaction: do not re-use or re-challenge.
Renal impairment: delayed clearance, dose uncertainty, and a potassium load from the salt.
Active liver disease: liver-injury risk — avoid.
Blood-sugar-prone: fasting low blood sugar — take with food and monitor.

10B. Pregnancy & Lactation

P-3 — Insufficient controlled data (precautionary) Lactation transfer: T-U (unstudied for supplementation)

Pregnancy: human safety is not established; with no proven benefit to weigh against the unknowns, supplemental PABA should be avoided in pregnancy absent a clear medical indication — route decisions to the obstetric team. Lactation: it is not known whether PABA is excreted in breast milk or its effects on a nursing infant; route to an IBCLC/pediatrician, with LactMed and OTIS MotherToBaby as references. European Medicines Agency. Potassium para-aminobenzoate — CMDh Scientific Conclusions. Open Source ↗ Centers for Disease Control and Prevention. Breastfeeding & Medications. Open Source ↗

Routing: pregnancy questions → obstetrician/midwife; lactation/infant-exposure → IBCLC/pediatrician; antibiotic interactions → prescriber/pharmacist.

11. Co-Use & Combinations

Key Takeaway

The "PABA aids folate utilization" claim is unsubstantiated in humans. Historical vitamin-E or B5 combinations show no documented harm. The combinations to avoid are sulfonamides/dapsone/PAS, antidiabetics without monitoring, and high-dose use while fasting.

11A. Co-Use Notes

Folate (B9): PABA is a microbial folate precursor, not a human cofactor — the "aids folate utilization" marketing claim is unsubstantiated in humans.
Vitamin E / vitamin B5: historical combinations (Peyronie's; gray hair) with no documented harmful interaction.
Supplement–supplement interactions are otherwise largely unstudied.

11B. Combinations to Avoid

Sulfonamides / dapsone / para-aminosalicylic acid — antifolate antagonism (must not be used with sulfonamides).
Antidiabetics / insulin without glucose monitoring — additive low blood sugar.
High-dose PABA while fasting or unwell — low-blood-sugar risk; other hepatotoxins / alcohol — theoretical additive liver risk.

Krátký M, et al. 4-Aminobenzoic Acid Derivatives. Open Source ↗

12. Lab Monitoring

Key Takeaway

PABA is itself a diagnostic marker, so supplement use confounds urine-completeness and pancreatic-function testing and certain colorimetric assays. Check liver blood tests if symptoms arise (first ~8 weeks); monitor glucose in at-risk users.

12A. Monitoring

Routine monitoring is not standard for supplement use, but: check liver blood tests if any liver-related symptoms develop (the first ~8 weeks carry the highest risk), and monitor blood glucose in those prone to low blood sugar. Critically, record PABA use whenever a urine-completeness or pancreatic-function test is planned. Meyer B, Gyr K. Oral NBT-PABA pancreatic function test. 1987. Open Source ↗

12B. Lab Interference

Test	Effect	Note
24-hour-urine-completeness marker	Confounded	PABA is the marker itself — supplement use invalidates interpretation
NBT-PABA / bentiromide pancreatic test	Confounded	Exogenous PABA distorts urinary PABA recovery
Colorimetric arylamine assays	Interference	Shared arylamine chemistry (also confounded by certain foods/drugs)
Liver blood tests	May be elevated	In the rare event of immunoallergic liver injury

13. Historical Context

Key Takeaway

No traditional-medicine lineage — PABA is a 20th-century compound mislabeled a "vitamin," used as a sunscreen and a niche antifibrotic drug, with each wave of use outrunning the evidence.

PABA has no folk-medicine tradition. Identified as part of the folate molecule in the early 20th century, it was incorrectly labeled "vitamin B10," promoted for gray hair in the 1940s–50s, and used as a sunscreen ingredient before being removed over allergy and skin-reaction concerns. Its prescription salt found a niche for fibrosing conditions, but the controlled evidence has been weak — a recurring lesson that enthusiasm and long use do not establish efficacy. U.S. Food and Drug Administration. Sunscreen Drug Products — Proposed Order (OTC000008). Open Source ↗

14. Quality Control

Key Takeaway

PABA is a well-defined compound with a USP monograph; verify the form (free PABA vs the potassium salt), third-party testing, and a modest dose. The threshold question remains whether to use it at all.

Specification. PABA is a well-defined chemical with an established USP monograph (aminobenzoic acid); specify free PABA for the supplement (distinct from the prescription potassium salt), with third-party identity/purity testing and a clearly labeled, modest dose. The potassium salt additionally carries a potassium load relevant in renal impairment. PubChem (NIH). Compound Summary: 4-Aminobenzoic acid (CID 978). Open Source ↗

Positioning. Given the absence of proven supplement benefit and the documented risks, the most important quality decision is whether PABA is warranted at all; the supplement should never be substituted for prescribed care. U.S. Food and Drug Administration. Drug Efficacy Study Implementation: Potassium Aminobenzoate. Federal Register. Open Source ↗

✓ Last Reviewed: June 2026