Finasteride and PSA blood tests: what the number means

Finasteride blocks type II 5-alpha-reductase and lowers dihydrotestosterone. Prostate-specific antigen (PSA) production is androgen-sensitive, so the blood number typically falls after months on the drug. U.S. prescribing information for finasteride 1 mg (male pattern hair loss) and 5 mg (BPH) has long told clinicians to expect about a 50% PSA drop after roughly a year and to interpret serial values with that effect in mind. Dutasteride, which blocks both enzyme isoforms, also lowers PSA. The important sentence is not a forum mnemonic. It is: whoever orders or reviews your PSA needs to know you take a 5-ARI, the dose, and when you started.

A lower PSA on finasteride is not proof that the prostate is healthy, and a rising PSA on treatment is not something to explain away as 'just hair meds.' Screening guidelines still treat PSA as a shared decision with age, family history, race, prior biopsies, and symptoms — finasteride is one more variable, not a reason to hide the test. Some clinicians double a stable on-treatment PSA to compare with untreated cutoffs; others watch the trend on the same lab. Do not invent your own conversion on a patient portal and then skip the appointment. Biotin megadoses can interfere with some immunoassays; list every supplement too.

This is not medical advice and not a cancer screening plan. Do not start, stop, or time finasteride around a PSA without the clinician who will read the result. People who can become pregnant must not handle crushed or broken finasteride tablets. If you donate blood, tell the collection staff about finasteride — deferral rules exist because of birth-defect risk to a transfusion recipient, which is a separate issue from PSA. Sudden urinary symptoms, bone pain, or a rapidly rising PSA belong in clinic, not in a hair-loss comment thread.

Fontes: StatPearls (NIH) ↗

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