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Hairmetry

Encyclopedia

Every molecule that touches your hair

From proven medicines to kitchen-cupboard oils, with the studies behind each one.

36 entries

A

  • drug with hair side effects

    Acitretin

    A prescription retinoid for severe psoriasis whose most common side effect is hair thinning, and which must never be used in pregnancy.

  • other

    Aminexil

    Aminexil is a minoxidil-like cosmetic sold as an anti-shedding ampoule, with no human trial and a rat study that found it the weakest of the products tested.

  • botanical

    AnaGain

    AnaGain is a pea sprout extract with a small maker-run study and mouse data, plausible and low risk but without an independent controlled trial.

  • drug with hair side effects

    Anticoagulants (heparin, warfarin, DOACs)

    Blood thinners that can cause shedding about 3 months after starting, which usually reverses and is never a reason to stop on your own.

  • drug with hair side effects

    Antithyroid drugs (carbimazole, methimazole, propylthiouracil)

    Medicines for an overactive thyroid; shedding on them can come from the thyroid disease, an over-treated thyroid, or the drug, which is hard to separate.

  • botanical

    Ashwagandha

    A herbal root that lowers measured stress in short trials, with one small hair study and rare reports of serious liver injury.

B

  • drug with hair side effects

    Beta-blockers

    Heart and blood-pressure drugs that rarely cause reversible shedding, based on old case reports only.

  • supplement

    Biotin

    A B vitamin that restores hair only in the rare people who are deficient, and that can scramble thyroid and heart blood tests at the doses sold for hair.

  • botanical

    Black seed oil

    Black seed oil's hair reputation rests on animal work and a tiny open-label lotion study, with no independent controlled human trial.

C

  • growth stimulant

    Caffeine (topical)

    Caffeine in shampoos and leave-on liquids clearly stimulates hair follicles in the lab, but the human trials are small, mostly industry-run and mostly on blends.

F

  • supplement

    Folate (vitamin B9)

    A B vitamin that is sometimes low in people with hair loss, but not a hair-growth supplement if your levels are normal.

G

  • drug with hair side effects

    GLP-1 receptor agonists (semaglutide, tirzepatide)

    The new weight-loss injections list hair shedding as a side effect in about 3-6% of trial participants versus about 1% on placebo, far more often in women, and it appears tied to weight loss rather than toxicity to follicles.

H

I

  • supplement

    Iron and ferritin

    Low iron stores are common in people who shed hair, but no trial has shown that iron pills regrow hair, and nobody agrees on a hair-specific ferritin target.

  • drug with hair side effects

    Isotretinoin

    A prescription acne drug that causes shedding in a few percent of users and, far more seriously, severe birth defects.

L

  • supplement

    L-lysine

    An essential amino acid once paired with iron for women with shedding, with no recent independent trial.

  • drug with hair side effects

    Lithium

    A mood-stabilising medicine whose label lists hair thinning, with figures ranging from no excess in trials to about 1 in 5 in older surveys.

M

  • supplement

    Marine protein supplements (Viviscal, Nourkrin)

    Branded fish- and shellfish-extract pills with positive but small, manufacturer-linked trials.

  • growth stimulant

    Melatonin (topical)

    Hair follicles make their own melatonin, and a small 2004 trial found a scalp solution raised the share of growing hairs in women, but later studies are uncontrolled and sponsored by the maker.

  • drug with hair side effects

    Methotrexate

    A weekly immune-suppressing medicine that thins hair in a few percent of users, and is also used off-label for severe alopecia areata.

  • pathway modulator

    Midodrine

    A blood-pressure pill that gives many people goosebumps and a tingling scalp because it grips the tiny muscle at each hair; related drugs briefly cut shedding during brushing, but midodrine itself has never been tested on hair.

  • growth stimulant

    Minoxidil

    The most widely used hair-growth treatment, available as a cheap over-the-counter lotion or foam and as a prescription tablet, with a mechanism that is still only partly understood.

N

  • other

    Niacinamide

    Niacinamide is a safe, cheap vitamin B3 form found in many hair serums, but no trial shows it grows hair on its own.

O

  • supplement

    Omega-3 fatty acids

    Fish-oil fats whose only hair evidence is a branded omega-3/6 plus antioxidant product tested in women.

P

  • protein or peptide

    Procapil

    Procapil is a branded trio of a biotin-linked peptide, apigenin and oleanolic acid sold as a hair-anchoring active, with small studies that are mostly add-ons to other treatments.

R

  • botanical

    Redensyl

    Redensyl is a branded cosmetic blend marketed to wake follicle stem cells, with one small vehicle-controlled trial in a blend and several maker-linked open-label studies.

S

  • supplement

    Selenium

    An essential mineral with no proof that supplements regrow hair, and a well-known cause of hair loss in excess.

  • antiandrogen

    Spironolactone

    A cheap blood-pressure pill that blocks androgen receptors and is the most widely used off-label hormonal treatment for women's pattern hair loss.

  • drug with hair side effects

    SSRIs and other antidepressants

    Antidepressants rarely cause hair loss; in a million-user database, bupropion carried the highest risk and fluoxetine and paroxetine the lowest, but absolute risk is small and depression itself also sheds hair.

  • other

    Stemoxydine

    Stemoxydine is a cosmetic compound from L'Oréal pitched as mimicking the low-oxygen niche of follicle stem cells, with no peer-reviewed trial.

T

  • drug with hair side effects

    Topiramate

    An epilepsy and migraine pill sometimes floated as a topical hair grower, although nobody has ever tested it on scalp hair; the real hair signals are reversible shedding, one case of overlong eyelashes and a small open trial in compulsive hair-pulling.

U

  • supplement

    Urolithin A

    A gut-bacteria product of pomegranate and walnut compounds, sold as a mitochondria longevity supplement, protected human hair-papilla cells from oxidative damage in a brand-new 2026 company-linked paper, with no controlled human hair trial.

V

  • supplement

    Vitamin A

    Too much preformed vitamin A can make hair fall out, so extra vitamin A in a hair supplement is more likely to harm than help.

  • supplement

    Vitamin B12

    A real but uncommon cause of hair loss when deficient, with no evidence that extra B12 helps hair if your levels are normal.

  • supplement

    Vitamin D

    Hair loss goes with low vitamin D and the receptor is needed for the hair cycle, but no good trial shows supplements regrow hair if you are not deficient.

Z

  • supplement

    Zinc

    True zinc deficiency causes hair loss that zinc fixes, but zinc has not been shown to regrow hair in people who are not deficient, and too much causes copper deficiency.