The downside is Saw Palmetto reduces androgenic receptor sites, but it has an anti-estrogenic effect.
F.Di Silverio, et al., "Evidence that Serenoa Repens Extract Displays Antiestrogenic Activity in Prostratic Tissue of Benign Prostatic Hypertrophy," Eur. Urol. 21(1992):309-314
SP can inhibit DHT, which means it can reduce AGA (androgenetic alopecia) hair loss. Extracts of SP interfere with the metabolism of DHT and stop the action of 5 alpha-reductase enzymes.
Other DHT inhibitors are, Pygeum, Green Tea, He Shou Wu and silica.