ASK PRESCRIBER: no formal interaction between saw palmetto and finasteride is listed in the Propecia SmPC, but saw palmetto is thought to act on the same hormone pathway, the evidence for it in hair loss is limited, and supplements are not checked like medicines. Tell your prescriber before combining them.
Mechanism
Saw palmetto is a berry extract sold mainly as a food supplement. It is described as having antiandrogenic properties, and the research it draws on suggests it inhibits 5-alpha-reductase, the same enzyme finasteride blocks to lower DHT. Taking both may therefore duplicate the mechanism rather than add something new. There is no good evidence on what the combination does, for better or worse.
The evidence for saw palmetto itself is thin. A 2020 systematic review in Skin Appendage Disorders (Evron et al.) found some positive small studies in hair loss but concluded that robust high-quality data are lacking. The US National Center for Complementary and Integrative Health says the evidence for male-pattern hair loss is 'too limited to allow conclusions to be reached'. For prostate symptoms, a 2023 Cochrane review found that saw palmetto on its own provides little or no benefit.
Safety: adverse effects in studies are mild and infrequent, such as digestive upset, dizziness and headache. The Evron review cites a study finding saw palmetto did not alter CYP3A4 or CYP2D6 activity, so a chemical interaction affecting finasteride levels seems unlikely, and it notes isolated case reports, including bleeding during surgery. Quality is the bigger unknown. In the UK, food supplements are regulated as food, not medicines, with no pre-sale approval, and the seller is responsible for their safety. Products registered as traditional herbal medicines carry a THR number, but that registration is based on traditional use, not clinical trials of effectiveness.
Practical advice
Tell your prescriber about saw palmetto and any other supplements in your assessment. It is not a reason to refuse treatment, but it helps the doctor see the full picture, particularly if you develop side effects.
Do not use saw palmetto as a reason to change your finasteride dose, and do not replace a prescribed medicine with a supplement without talking it through. Finasteride carries MHRA warnings (Drug Safety Updates of 29 April 2024 and 11 May 2026) about psychiatric reactions including depression and suicidal thoughts, and sexual dysfunction which may persist after discontinuation; see finasteride 1 mg and the MHRA safety updates.
If you are having surgery, including a hair transplant, tell the surgical team about any herbal supplements you take (see pre and post-transplant treatment).
Choosing not to take a supplement is reasonable. Many hair supplements promise more than the evidence supports; the same applies to biotin. If you would like to explore options with a doctor, you can start a free online assessment.