Biotin for hair: what it really does, when it's worth taking and when it's money down the drain
Quick answer
Biotin (vitamin B7, also called vitamin H) is needed to make keratin, the protein your hair is made of, and a deficiency causes hair loss and brittle hair. But biotin deficiency is rare: a normal diet covers it, and EFSA sets adequate intake for adults at 40 micrograms a day. In people without a deficiency, there's no solid evidence that taking more biotin makes hair grow or slows male pattern baldness. Supplementing makes sense if you've been on a very restrictive diet, take certain medicines, drink a lot of alcohol or have absorption problems, and as part of a complete hair supplement with zinc, vitamin D and other actives. One warning: high doses of biotin can skew blood test results (thyroid, troponin), so tell your doctor before any blood test.
Search for "biotin" in any shop and it looks like the miracle ingredient for hair, nails and life in general. Gummies, capsules, "biotin" shampoos, even biotin water. Everyone sells it. Hardly anyone tells you what it actually does.
Here's the version without the marketing: biotin is essential for hair, but you probably already have all you need. And that's the industry's trick. Let's look at what it does, when you're short of it, how much you need, what the evidence says about taking more, and how we use it in Growzilla, which contains it too, but for a different reason.
- What biotin is and what it has to do with your hair
- When you're short of biotin (and why that's almost never you)
- Does biotin make hair grow? What the evidence says
- How much biotin you need
- Which foods contain biotin
- Biotin and blood tests: the warning that matters
- Why Growzilla contains biotin (and why it isn't the main ingredient)
- FAQ
- Sources and evidence
What biotin is and what it has to do with your hair
Biotin is vitamin B7 (it's also called vitamin H, from the German "Haar und Haut", hair and skin, which rather gives the game away). It's water-soluble, your body doesn't store it, and it works as a helper to enzymes involved in breaking down fats, sugars and amino acids. Among those amino acids are the ones that make up keratin, which is what your hair is made of.
No biotin, no proper keratin. That's why a deficiency leads to thin, brittle hair that falls out, nails that break and dermatitis. All true so far. The question is how many people actually have that deficiency. And the answer is: almost nobody.
When you're short of biotin (and why that's almost never you)
Biotin deficiency is rare because biotin is in loads of foods and your gut bacteria make some of it. The situations where you can genuinely run short are very specific:
- Very restrictive or chaotic diets for months on end.
- Heavy, regular drinking (it reduces absorption).
- Raw egg whites by the bucketload. The avidin in egg white locks biotin up. It's the Rocky raw-egg myth: bad for your hair as well as your stomach. Cook them and the problem goes away.
- Some medicines taken long term: anticonvulsants, long courses of antibiotics, isotretinoin.
- Gut absorption problems, bariatric surgery, inflammatory bowel disease.
- Pregnancy and breastfeeding (not your problem, but for the record).
If you're not on this list and eat a reasonably varied diet, your biotin level is very likely normal, and taking extra biotin on its own won't change a thing for your hair. And if what brought you here is suddenly losing a lot of hair, it's most likely something else: read what telogen effluvium is and why hair falls out more in autumn.
Does biotin make hair grow? What the evidence says
This is the bit some competitors would rather you skipped.
Review by Patel and colleagues (Skin Appendage Disorders, 2017)
The authors searched for every published case in which biotin had improved hair or nails. They found 18. In all 18 there was an underlying problem (a biotin deficiency or a specific disease). Their conclusion: there isn't enough evidence to support biotin supplements in healthy people. A later review of vitamins, minerals and hair loss (Almohanna and colleagues, 2019) points the same way: micronutrient deficiencies can play a part in hair loss, but there are no trials showing that supplementing them without a deficiency makes hair grow.
What does exist in the EU is an authorised health claim for biotin: "contributes to the maintenance of normal hair". Look closely at that word: maintenance. Not growth, not less shedding, not more density. Any product promising that biotin will make your hair grow is saying something EU law doesn't allow it to say.
And on androgenetic alopecia (male pattern baldness, the receding temples and thinning crown kind): biotin doesn't touch DHT, doesn't extend the growth phase and doesn't thicken follicles. It simply isn't for that.
How much biotin you need (and why 10,000 µg is marketing)
EFSA sets adequate biotin intake for adults at 40 micrograms a day. Micrograms. A normal diet covers that easily: two eggs already get you about halfway.
Now look at the labels on biotin supplements "for hair": 5,000 µg, 10,000 µg. That's 125 to 250 times adequate intake. Because biotin is water-soluble, the excess leaves in your urine and isn't toxic, but it doesn't do any more either: no study shows that 10,000 µg works better than 50 in someone without a deficiency. Megadoses are a marketing argument, not an effective dose.
40 µg/day = enough (EFSA) 2 eggs ≈ 20 µg 10,000 µg = 250 times what you need
Doses of 1,000 to 3,000 µg in a hair supplement serve a different purpose: covering any gaps in your diet with room to spare, without joining the megadose arms race, which also brings a problem we'll get to next.
Which foods contain biotin
If your diet looks something like this, you're not short of biotin:
- Eggs (the yolk; cooked egg white is no problem).
- Nuts and seeds: almonds, peanuts, walnuts, sunflower seeds.
- Pulses: lentils, chickpeas, soya.
- Liver and offal (few people eat them, but they're the richest source).
- Salmon, sardines.
- Avocado, sweet potato, mushrooms, bananas.
If your diet looks more like a motorway service station menu, the conversation isn't about biotin. It's about your diet. And for your hair, total protein, iron and zinc matter more than B7.
Biotin and blood tests: the warning that matters
High doses of biotin interfere with many lab tests that use biotin in their technology. They can give false results for thyroid tests (TSH, T4), troponin (the heart attack marker), vitamin D and some hormones. The US FDA issued a warning in 2017 after a patient taking high-dose biotin died when their troponin test came back falsely low. It updated the warning in 2019.
What to do: if you take any supplement containing biotin, tell your doctor and the lab before a blood test, and ask whether you should stop taking it a few days beforehand. The FDA itself says there isn't enough data to know how long a break prevents the error, so the important thing is that they know. And if you end up in A&E with chest pain, mention it.
Why Growzilla contains biotin (and why it isn't the main ingredient)
Growzilla contains 2.5 mg of biotin (2,500 µg) per daily dose. After what you've just read, you'll understand we don't put it there to make your hair grow. We put it there so that, if your diet has gaps, biotin isn't one of them. That's all.
The ingredient Growzilla really exists for is a different one: saw palmetto standardised to 85%, 320 mg, the dose used in clinical trials on androgenetic alopecia. Around it are pumpkin seed (400 mg), nettle (200 mg), Pygeum, zinc as bisglycinate (10 mg) and vitamin D3 (25 µg), plus the biotin.
What's in every daily dose
Saw palmetto320 mg, extract standardised to 85%. The dose used in clinical trials.
Pumpkin seed400 mg.
Nettle200 mg.
Pygeum africanum20 mg.
Zinc (bisglycinate)10 mg (100% NRV). Contributes to the maintenance of normal hair.
Vitamin D325 µg (500% NRV).
Biotin2.5 mg (5,000% NRV). Contributes to the maintenance of normal hair.
Copper + seleniumSelenium contributes to the maintenance of normal hair; copper to normal hair pigmentation.
Plus ginseng, ginkgo and green tea, for more than 20 micronutrients and extracts in total. NRV: nutrient reference value.
In other words: Growzilla isn't "biotin for hair". It's a hair supplement for men worried about hair loss that, among other things, makes sure biotin is covered. If all you want is biotin, buy eggs. If you want a supplement with saw palmetto at the dose used in the studies, then yes.
Sixty vegan capsules, two a day, one month. €34.99. And the realistic expectation: studies on saw palmetto talk about at least 4 to 6 months before you can judge. Anything less and you haven't really tried it.
Dr Marcel Guiu
Dr Marcel Guiu Ortín is a medical doctor (@marcelguiu) who reviewed our guide to hair loss in men.
In this video he explains what happens when hair falls out and what mix of ingredients goes into Growzilla. One minute, no jargon. The video is in Spanish.
Dr Marcel Guiu on hair loss and Growzilla (in Spanish).
€34.99
Growzilla
Hair supplement for men worried about hair loss. More than 20 micronutrients and botanical extracts.
- Saw palmetto 320 mg at 85%
- Zinc, D3 and biotin
- 60 vegan capsules = 1 month (2 a day)
Free shipping from €59.
And on the outside, the usual: a supplement works best when your scalp is in good shape. Hairicane in the shower and Follicool afterwards are the routine that goes with Growzilla.
FAQ about biotin and hair
Does biotin make hair grow?
Only if you're deficient in biotin, which is uncommon. In people with normal levels, there's no evidence that taking more biotin makes hair grow or slows hair loss. The claim authorised in the EU is that biotin "contributes to the maintenance of normal hair".
How much biotin should you take a day for your hair?
Adequate intake for adults is about 40 µg a day (EFSA), and a normal diet covers it. Supplements usually contain between 1,000 and 10,000 µg; the excess isn't toxic, but there's no evidence that megadoses work any better.
How long does biotin take to work?
If you're deficient, the improvement in your hair shows after 3 to 6 months, which is how long new hair takes to grow. If you're not deficient, there's no effect to wait for.
Does biotin have side effects?
At usual doses, no: it's water-soluble and the excess leaves in your urine. The real risk is that high doses skew thyroid, troponin and other lab results. Tell your doctor and the lab before a blood test and ask whether you should stop a few days beforehand.
Biotin or zinc for hair?
Both matter, and zinc deficiency is far more common than biotin deficiency, especially in vegetarians and athletes. A sensible hair supplement contains both at reasonable doses, not a megadose of one.
Does biotin help with male pattern baldness?
It doesn't act on DHT or on miniaturised follicles, which are what drive male pattern baldness. That's what minoxidil and finasteride (medicines) are for, with studied extracts such as saw palmetto as support.
Which foods are highest in biotin?
Egg yolk, liver, nuts and seeds, pulses, salmon, avocado and sweet potato. Eggs and nuts every day already cover a good share of adequate intake.
Sources and evidence
The studies and documents this article is based on, so you can read them yourself:
- Patel D.P., Swink S.M., Castelo-Soccio L. A Review of the Use of Biotin for Hair Loss. Skin Appendage Disord (2017).
- Almohanna H.M. et al. The Role of Vitamins and Minerals in Hair Loss: A Review. Dermatol Ther (Heidelb) (2019).
- EFSA NDA Panel. Scientific Opinion on Dietary Reference Values for biotin. EFSA Journal (2014).
- Regulation (EU) 432/2012 — authorised health claims (biotin, zinc, selenium, copper).
- FDA. The FDA Warns that Biotin May Interfere with Lab Tests: FDA Safety Communication (2017, updated 2019).
Neither villain nor hero
Biotin is a basic building block you should already have covered. If you want to do something about hair loss, the question isn't how much biotin, it's what else is in the capsule.
See GrowzillaNote: this article is for general information only and does not replace an assessment by a healthcare professional. Growzilla is a food supplement: it should not be used as a substitute for a varied, balanced diet and a healthy lifestyle, or for medical treatment. Do not exceed the recommended daily dose. If you take medication (especially blood thinners) or have a medical condition, check with your doctor before taking it. If you're having a blood test, tell your doctor you take biotin.