Hair supplements (biotin, saw palmetto…): what works and what does not

You go into the pharmacy for something else and come out with a tub of hair capsules. Biotin, plant extracts, complexes with names that sound like a serious laboratory. The promise is always much the same: less shedding, more density, stronger hair. The reasonable question is how much of that is backed up and how much is marketing on a pretty bottle. We are not going to sell you hope here, nor knock everything down in one go: we are going to look at what studies have found when they have set out to test it properly, and separate what is actually known from what is repeated out of habit.

Why hair falls out and what can be acted on

Before talking about bottles, it helps to understand the ground. In non-scarring alopecia the hair follicle remains intact, which leaves the door open to possible regrowth; this group includes androgenetic alopecia, telogen effluvium and alopecia areata (Cosmoderma, 2024). The most common is androgenetic alopecia, the gradual recession associated with age and the hormone DHT. Its prevalence is high in Spain according to the consensus of the Spanish Hair Disorders Group of the AEDV (Actas Dermo-Sifiliográficas, 2024), and a secondary review puts it, as a rough figure, at up to 80% of men and 42% of women over their lifetime (Cosmoderma, 2024). The fact that the follicle is alive is the good news: it means there is something to act on. The question is what with.

What the evidence says about supplements

The most orderly piece of work on this is a systematic review that brought together 30 articles, including randomised trials, non-randomised studies and case series (Drake et al., JAMA Dermatology 2023). Its nuanced conclusion is useful: among the higher-quality studies, some products showed a potential benefit. Names such as Viviscal, Nourkrin, Nutrafol, Lamdapil and Pantogar appear, along with combinations of capsaicin and isoflavone, omega-3 and omega-6 with antioxidants, an apple nutraceutical, total glucosides of paeony, compound glycyrrhizin, zinc, tocotrienol and pumpkin seed oil (Drake et al., 2023). Others, such as kimchi and cheonggukjang, vitamin D3 or Forti5, had only low-quality evidence of improving the course of the problem.

The honest summary is this: there are signals, not miracles. A recent meta-analysis of commercial supplements found improvements in some hair parameters, but not in total hair count, and describes its results as preliminary (Alanazi et al., J Cosmetic Dermatology 2026): modest is the key word. They do not reverse alopecia. And be careful with diet: no dietary intervention study met the review's inclusion criteria (Drake et al., 2023), so the idea that eating differently slows hair loss has, as things stand, no firm support. On the reassuring side, the safety profile is good: adverse effects of the supplements assessed were rare and mild (Drake et al., 2023).

Biotin: the case that deserves a section of its own

Biotin is the queen of hair supplements, and also the one that calls for the most caution. Not because of its efficacy, but because of a little-known detail: many hair, skin and nail products contain biotin at up to 650 times the recommended daily intake (FDA, 2017). That excess is not dangerous in itself, but it can interfere with laboratory tests. Biotin is used in hormone tests and in cardiac markers such as troponin, and high blood levels can distort those immunoassays and lead to misdiagnosis. The FDA even reported a death in which interference with a troponin test led to a heart attack going undiagnosed (FDA, 2017).

The practical point is simple: if you take biotin and are about to have a blood test, tell whoever is requesting it. With doses of up to 5-10 mg it is usually enough to take the sample at least 8 hours after the last dose, and with high doses it is advisable to stop it at least two days beforehand, sometimes up to a week (JCAD, 2024). As for its efficacy as such, the uncomfortable part is that there is no solid evidence that biotin makes hair grow in people who are not deficient. In other words: if your levels are normal, taking more will not give you back density.

And what does have approval: minoxidil and finasteride

It is worth setting supplements against the treatments that do have regulatory approval, even though they are not the subject of this article. Topical minoxidil is the only FDA-approved treatment for androgenetic alopecia in both men and women; it started life as an oral antihypertensive, and its effect on body hair led to the development of the topical solution, approved at 2% in 1988 for men and in 1991 for women (Dias et al., Frontiers in Pharmacology 2025). The 5% formulations consistently increase hair count, with variations depending on the activity of a follicular enzyme (Dias et al., 2025). Low-dose oral minoxidil at 5 mg a day showed similar, not superior, efficacy to 5% topical minoxidil in men (Penha et al., JAMA Dermatology 2024), and its most frequent adverse effect is hypertrichosis, with cardiovascular events being uncommon at low doses.

Finasteride, from the group of 5-alpha reductase inhibitors, blocks the conversion of testosterone to DHT (summary of product characteristics, CIMA-AEMPS). At 1 mg a day it is a first-line treatment for male androgenetic alopecia and the only oral treatment with FDA approval. An important safety point is in order here: in 2025 the AEMPS confirmed a risk of suicidal ideation in patients treated with finasteride, mainly for alopecia, and cases of sexual dysfunction that could contribute to depressive symptoms have been reported; 1 mg packs will include a patient information card (AEMPS, 9 May 2025). The frequency of that suicidal ideation is considered unknown, as it cannot be estimated from the available data. As for sexual effects, the summary of product characteristics records 3.8% compared with 2.1% on placebo during the first 12 months, an incidence that falls to 0.6% over the following four years (CIMA-AEMPS). No link has been found between topical finasteride or dutasteride and suicidal thoughts, although, given the similar mechanism, the AEMPS considers it a possible class effect (AEMPS, May 2025). All of this is precisely why these medicines require medical assessment and follow-up, something an over-the-counter supplement does not provide.

In summary, and what you can do today

What to remember is simple: hair supplements offer, at most, a modest effect with specific brands, they do not reverse alopecia, and high-dose biotin can cause you problems with a blood test. If what you want is to really slow down hair loss, what does exist today in Spain is medical hair loss treatment, with a prior assessment, a prescription when appropriate from a registered doctor and ongoing follow-up: that is where it is decided what makes sense in your particular case and with what safeguards. With AiON you can check in a few minutes whether you are eligible and take the first step with sound judgement, not blindly.