Biotin

Biotin (a B vitamin, sometimes labeled vitamin H) is sold as a hair-growth fix, but unless you are actually deficient, which is rare, it almost certainly will not do that - and you should stop taking it, especially before any blood test. Biotin does not grow hair in people who are not low on it. The one place it earns its keep is brittle nails. In small older trials, 2.5mg daily made nail plates 25% thicker. The hair-growth evidence is basically limited to people with a confirmed deficiency, or to multi-ingredient formulas where you cannot tell what the biotin itself did. And there is a real safety catch: the FDA has put out two safety communications (2017, 2019) because high-dose biotin skews lab tests. One patient died from a missed heart attack when their troponin read falsely low. It can also fake Graves' disease on a thyroid panel, which sends people into unnecessary scans, medications, and surgeries.

On hair growth specifically, the evidence is much thinner. When reviews find any improvement, it shows up in people who had an underlying condition or a confirmed biotin deficiency to begin with. What is missing is good trials showing it works in healthy people with normal biotin levels. One caveat worth knowing: Trueb 2016 (PMID: 27601860, n=541 women with hair loss complaints) found that 38% had measurable biotin deficiency (<100 ng/L serum biotin), so subclinical deficiency may be more common in people seeing a dermatologist than you would assume. Trueb himself warned against reaching for biotin indiscriminately and said to confirm a deficiency in the lab before supplementing.

The glowing trials people cite are almost always for multi-ingredient complexes, not biotin on its own. A 2021 double-blind RCT (PMC11694638, n=65) reported a 10.1% increase in terminal hair density versus a 2% decrease on placebo (p<0.001), but that product also contained zinc, tocotrienols, and astaxanthin alongside the biotin. You cannot pin the result on the biotin. And since biotin deficiency is rare in the general population, most healthy people taking it are unlikely to notice anything.

Here is the safety issue marketing rarely mentions. Above 5,000mcg, biotin interferes with blood tests that use streptavidin-biotin technology. In sandwich assays (like troponin), it pushes the number falsely low, which can hide an active heart attack. In competitive assays (like Free T4, Total T3, estradiol), it pushes the number falsely high. The FDA issued its first safety communication on November 28, 2017, set off by a confirmed patient death from a missed heart attack (myocardial infarction) caused by falsely low troponin. It updated that warning in November 2019, still concerned.

The downstream mess is serious. Falsely low TSH plus falsely high Free T4/T3 is the exact pattern of Graves' disease. The medical literature documents healthy (euthyroid) patients sent for unnecessary radioactive iodine scans, put on anti-thyroid drugs, even scheduled for thyroid removal, all from biotin-induced lab artifacts. False PSA readings can also hide a returning prostate cancer.

The mega-doses you see everywhere, 8,000-10,000mcg, buy you nothing over the 2,500mcg used in the research, and they add risk of lab interference and possible acne. Biotin clears fast (half-life around 2 hours), so at everyday nutritional doses (30-150 mcg) the interference risk is basically nonexistent. The danger lives at supplement-level doses of 2,500mcg and up.