Biotin for Hair Growth: What the Evidence Shows

Short answer: For most people, biotin probably won't make hair grow faster or thicker. The best placebo-controlled study found no difference between biotin and placebo, S04 and in a small 2024 trial in healthy men, biotin alone didn't change how fast hair grew. S05 Biotin does help hair when someone is truly deficient or has certain rare conditions, S01 S03 but deficiency is rare in people eating a normal diet. S01 The bigger issue is safety: the high doses in many hair supplements can cause falsely high or low results on some lab tests, including a heart-attack test. S01 S06

Biotin, also called vitamin B7, is one of the best-known ingredients in hair, skin and nail supplements. Here's what the research actually tested, who might benefit, and what to know before you take a high-dose pill.

Why biotin became a hair supplement

The link comes from deficiency. When people don't get enough biotin, the signs can include thinning hair that may progress to losing all body hair, a scaly red rash around the eyes, nose and mouth, and brittle nails. S01 It's a reasonable leap to think that if too little biotin causes hair loss, more biotin might grow more hair. That's why supplements are so often promoted for hair, skin and nails. S01

The problem is that the leap doesn't hold up for people who aren't deficient. The NIH Office of Dietary Supplements (ODS) says hair, skin and nail claims for biotin are supported, at best, by only a few case reports and small studies. S01

What the research shows

Reviews: improvement only with an underlying problem

A 2017 review found 18 reported cases of people taking biotin for hair or nail changes. S03 Every one of them had an underlying condition causing poor hair or nail growth, and all improved with biotin. S03 The authors concluded there was limited research to support biotin in healthy people. S03

A 2024 review went further, looking only at studies of oral biotin for hair growth or quality, not case reports. Just three studies qualified. S04 The highest-quality one, a double-blind, placebo-controlled trial, found no difference in hair growth between biotin and placebo. S04 The other two studied specific groups (people taking the acne drug isotretinoin and women after weight-loss surgery), were open to bias, and didn't show striking results. S04 The authors described a large gap between public perception of biotin and the scientific literature. S04

A small 2024 trial in healthy men

A randomized crossover trial in Brazil compared 5 mg of oral biotin, 5% topical minoxidil, and both together in 10 healthy men, using each for 14 days. S05 Biotin on its own didn't change hair growth rate: about 2.5 mm a week with or without it. S05 Minoxidil alone didn't make a significant difference in that short window either, but the combination did increase growth rate. S05 With only 10 men and two-week treatment periods, it's an early signal, not proof that biotin adds anything to minoxidil.

Where biotin clearly helps

The ODS points to a few situations where biotin matters for hair: S01

• Uncombable hair syndrome, a rare hair-shaft disorder: case reports in children found 3 to 5 mg a day improved hair after 3 to 4 months. S01
• Biotinidase deficiency, a rare inherited disorder that stops the body from releasing free biotin, causing deficiency despite a normal diet. S01
• Other causes of low biotin, which the ODS lists as groups at risk; for example, at least a third of pregnant women develop marginal biotin deficiency even with normal intakes, though the clinical significance isn't clear. S01

Evidence at a glance

How much biotin do you need?

Adults need about 30 mcg of biotin a day (35 mcg when breastfeeding). S01 That's the adequate intake, not a target to exceed. Many foods contain some biotin; the richest sources include organ meats, eggs, fish, meat, seeds, nuts and some vegetables, such as sweet potatoes. S01

One food quirk: raw egg whites contain avidin, a protein that binds biotin and blocks its absorption. Cooking the eggs denatures avidin so it no longer interferes. S01

Hair supplements often contain far more. The FDA says it knows of many supplements with 20 mg of biotin, some with up to 100 mg per pill, and labels that recommend several pills a day. S06 For comparison, 20 mg is more than 650 times the daily adequate intake of 30 mcg (0.03 mg). S01 S06

The lab-test catch

High-dose biotin isn't known to be toxic. Studies have found no adverse effects at 10 to 50 mg a day. S01 The risk is different: biotin can interfere with many lab tests that rely on biotin-based chemistry. S01

• Thyroid tests. Case reports describe results falsely suggesting Graves' disease or severe hyperthyroidism in people taking 10 to 300 mg a day. Even a single 10 mg dose has interfered with thyroid tests taken within 24 hours. S01
• Heart tests. Biotin can cause falsely low results on troponin tests, which help diagnose heart attacks. The ODS reports that, according to the FDA, a patient taking high-dose biotin died after a troponin test gave a falsely low result. S01 The FDA has continued to receive reports of biotin causing falsely low troponin results. S07
• Other tests. Interference can also affect a heart-failure marker (NT-proBNP) and other hormone and vitamin tests, producing falsely normal or abnormal results. S01

The FDA advises talking to your doctor if you take biotin or are thinking about it, and notes that the amount can be hard to tell from a supplement's name. S06 It also says there isn't enough information to know whether stopping biotin for a certain number of hours before a test prevents wrong results. S06 So the practical step is simple: tell whoever orders your blood work about every supplement you take, including multivitamins and prenatal vitamins. S02 S06

What to try instead

If your hair is thinning or shedding, the most useful step is finding out why. The American Academy of Dermatology (AAD) says losing 50 to 100 hairs a day is normal. S08 Shedding more than that, called telogen effluvium, often follows a stressor such as childbirth, and it usually stops on its own. S08 Hair loss, where hair stops growing, is different: hereditary hair loss continues without treatment, and the AAD recommends seeing a board-certified dermatologist. S08

For more on each path:

• Read our guide to telogen effluvium and how to approach hair care while shedding.
• See what the evidence says in our hair growth oils comparison.
• If you want a gentler wash routine for fine or thinning strands, see shampoo for thinning hair.

Frequently asked questions

Does biotin really help hair grow?

Not for most people. The highest-quality placebo-controlled study found no difference between biotin and placebo, and a small 2024 trial in healthy men found biotin alone didn't change hair growth rate. Biotin helps when hair problems come from deficiency or certain rare conditions.

How long does biotin take to work for hair?

There's no good evidence that it works in people who aren't deficient, so there's no reliable timeline. In children with the rare condition uncombable hair syndrome, case reports found improvement after 3 to 4 months of 3 to 5 mg a day.

How much biotin should I take for hair?

Adults need about 30 mcg a day, which most people get from food. Many hair supplements contain 20 mg or more, far above that amount, without good evidence of benefit. Ask your doctor before taking a high dose.

What are the side effects of biotin?

Studies have found no adverse effects at 10 to 50 mg a day. The main risk is that high doses can cause falsely high or low results on some lab tests, including thyroid and troponin tests used to diagnose heart attacks.

Should I stop biotin before a blood test?

Tell your doctor and the lab that you take it. The FDA says there isn't enough information to know whether stopping biotin for any number of hours before a test prevents incorrect results, so your care team should decide how to handle it.