The prescribing information for Propecia (finasteride 1 mg) says Propecia can affect the PSA blood test used for prostate cancer screening. Patients who have a PSA test are told to tell their healthcare provider they take Propecia, because it decreases PSA levels. The Prostate Cancer Prevention Trial tested finasteride 5 mg per day, not the 1 mg tablet.
What the label says about PSA
The label says any confirmed increase from the lowest PSA value while on Propecia may signal the presence of prostate cancer and should be evaluated, even if PSA levels are still within the normal range for men not taking a 5-alpha-reductase inhibitor. It also says other studies with Proscar showed it may also cause decreases in serum PSA in the presence of prostate cancer, and that these findings should be taken into account for proper interpretation of serum PSA when evaluating men treated with finasteride.
PSA numbers at 1 mg and 5 mg
| Source and dose | What it reports |
|---|---|
| Propecia label, finasteride 1 mg, clinical studies in men 18-41 years of age | Mean serum PSA decreased from 0.7 ng/mL at baseline to 0.5 ng/mL at Month 12 |
| Propecia label statement about Proscar, finasteride 5 mg, older men with benign prostatic hyperplasia (BPH) | PSA levels are decreased by approximately 50% |
| Randomized trial, finasteride 1 mg/day, men with androgenic alopecia | Within 48 weeks, median decrease in serum PSA of 40% (95% CI 34-46) at ages 40-49 and 50% (44-57) at ages 50-60 |
| Double-blind placebo-controlled study, finasteride 1 mg daily for 48 weeks, young men | Significant but small decrease in serum PSA (-0.2 ng./ml.), which reversed on discontinuation of the drug |
That trial's authors concluded that the existing recommendation for the adjustment of serum PSA concentration in prostate-cancer screening in men taking 5 mg/day finasteride should also apply to men taking the 1 mg/day preparation for male-pattern hair loss.
The Prostate Cancer Prevention Trial used 5 mg per day
The Prostate Cancer Prevention Trial (PCPT) randomly assigned 18,882 men 55 years of age or older with a normal digital rectal examination and a PSA level of 3.0 ng per milliliter or lower to finasteride (5 mg per day, not the 1 mg hair-loss dose) or placebo for seven years. In that finasteride 5 mg per day trial, prostate cancer was detected in 18.4 percent of men in the finasteride group with final-analysis data and 24.4 percent in the placebo group, a 24.8 percent reduction in prevalence over the seven-year period.
The Propecia label reports an increased risk of Gleason score 8-10 prostate cancer (finasteride 1.8% vs placebo 1.1%) with finasteride 5 mg/day (5 times the dose of Propecia) in the 7-year PCPT.
In the long-term follow-up report of the PCPT (finasteride 5 mg per day), prostate cancer was diagnosed in 989 of 9423 men (10.5%) in the finasteride group and 1412 of 9457 (14.9%) in the placebo group. Of the men evaluated, 333 (3.5%) in the finasteride group and 286 (3.0%) in the placebo group had high-grade cancer (Gleason score, 7 to 10), with a relative risk of 1.17 (95% CI, 1.00 to 1.37; P=0.05). The authors concluded that high-grade prostate cancer was more common in the finasteride group, but after 18 years of follow-up there was no significant between-group difference in overall survival or survival after the diagnosis of prostate cancer.
What the label and a 1 mg database study say about prostate cancer
The label states that 5-alpha-reductase inhibitors may increase the risk of development of high-grade prostate cancer. It adds that whether reduced prostate volume or study-related factors affected the results has not been established. After describing the PCPT and a dutasteride trial, the label says the clinical significance of these findings with respect to use of Propecia by men is unknown. It also says Proscar is not approved to reduce the risk of developing prostate cancer.
The label also lists male breast cancer, and breast tenderness and enlargement, among adverse reactions identified during post-approval use. In discussing breast cancer in men treated with Proscar, it states that the relationship between long-term use of finasteride and male breast neoplasia is currently unknown.
A 2026 matched-cohort database analysis of men with androgenic alopecia and at least 5 years of follow-up (observational, using diagnosis codes, so it cannot show cause and effect) found lower elevated PSA diagnosis and prostate cancer diagnosis rates in long-term finasteride 1 mg users than in matched men without finasteride use (2.9% vs. 4.4%; 0.9% vs. 1.8%).
What this does not tell you
The PCPT tested finasteride 5 mg per day in men 55 years or older. Its cancer figures are not results for the 1 mg tablet, and the label says their clinical significance for Propecia use is unknown. The PSA figures above come from different ages and doses, so they should not be combined. This guide does not say whether or when any man should have a PSA test. A licensed provider can advise on reading a PSA result while taking finasteride.