Saw palmetto, also known as Serenoa repens, Serenoa serrulata, and sabal palmetto shrub, is a plant of the family whose palm extract of the fruit has anti androgenic property. This material is used in the treatment of benign prostatic hyperplasia for many years, and has recently been proposed their use in the treatment of androgenetic alopecia.
Numerous drugs have the substance at different doses in the formulation, and recommend its use in the treatment of male and female androgenetic alopecia.
It can be administrated by both in topical and oral form. The exact mechanism of action of saw palmetto is unknown, although I imagine that is similar to that of finasteride by blocking the enzyme 5 alpha reductase and reducing the blood concentration of dihydrotestosterone.
To date there are very few studies that support the efficacy of saw palmetto in the treatment of androgenetic alopecia, so their use is still controversial.
Unwanted effects with the drug are rare, the most common minor gastric discomfort that can usually be relieved with their intake after meals.