Hair thinning and shedding can result from hormonal shifts (especially sensitivity to DHT), genetics, nutrient deficiencies, stress, and the natural aging of hair follicles. For most people it is gradual and multifactorial, which makes it hard to know what, if anything, actually helps.
Many of the supplements popularly marketed for hair health (biotin, extra vitamin D, iron, zinc) only have solid evidence in people who are frankly deficient in them, not as a general hair-thinning treatment, so they are not listed here. The supplements below are ranked based on the quality of the evidence and their expected impact on hair loss and thinning specifically.
