Could Saw Palmetto decrease the effectiveness of Finasteride?

I have not heard of any studies directly related to the combination use of finasteride and saw palmetto. However there are many people who do opt for the usage of saw palmetto instead of the finasteride.

Although we don't know exactly how saw palmetto (a.k.a. Serenoa Repens) works, it is assumed to either inhibit DHT, similar to finasteride, or to block alpha-adrenergic receptors, like tamsulosin. Both of these types of medications are used to treat benign prostatic hypertrophy but finasteride also helps male pattern hair loss.  There are small studies to support saw palmetto in hair loss and while there should not be any problem taking them both, I typically recommend patients use something like minoxidil, LLLT, or PRP in order to encourage hair growth by a different mechanism while using finasteride.Here are 2 nice articles on the action of Saw Palmetto:  1. Pharmacological effects of saw palmetto extract in the lower urinary tract Acta Pharmacol Sin. 2009 Mar; 30(3): 271–281. 2. Rossi A, et.al. Comparitive effectivenss of finasteride vs. serenoa repens in male androgenetic alopecia: a two-year study. Int J Immunopathol Pharmacol. 2012 Oct-Dec;25(4):1167-73.