Short answer: Both contain finasteride, a 5α-reductase inhibitor, but they are separate products for different approved uses.12 Propecia is a 1 mg tablet for male pattern hair loss in men. Proscar is a 5 mg tablet for symptoms of an enlarged prostate (BPH), alone or with doxazosin. Each label covers only its own use and strength. Neither has a boxed warning.
| Propecia | Proscar | |
|---|---|---|
| Tablet | Finasteride 1 mg1 | Finasteride 5 mg2 |
| Approved for | Male pattern hair loss in men only; not for women or children1 | Symptoms of BPH in men with an enlarged prostate, and lowering the risk of urinary retention and prostate surgery; with doxazosin, lowering the risk of BPH symptoms getting worse2 |
| Label dose | One 1 mg tablet once daily, with or without meals1 | One 5 mg tablet once a day, with or without meals, alone or with doxazosin2 |
| Time to judge the effect | Daily use for three months or more is generally needed before benefit is seen1 | A trial of at least 6 months was generally needed to judge symptom relief2 |
| Sexual side effects in label trials | Year 1 of three hair loss trials: decreased libido 1.8% vs 1.3% on placebo, erectile dysfunction 1.3% vs 0.7%1 | Year 1 of PLESS in men with BPH: impotence 8.1% vs 3.7% on placebo, decreased libido 6.4% vs 3.4%2 |
| Effect on PSA | Mean PSA fell from 0.7 to 0.5 ng/mL at month 12 in men aged 18 to 411 | PSA fell by about 50% within six months2 |
| Boxed warning | None1 | None2 |
They share the active ingredient, finasteride, but are approved for different conditions at different strengths.12 The Propecia label covers male pattern hair loss at 1 mg a day; the Proscar label covers BPH at 5 mg a day. The Propecia label describes the 5 mg dose used in a prostate cancer prevention trial as 5 times the Propecia dose.1 The trials behind each label enrolled different men: mostly younger men with hair loss for Propecia, older men with an enlarged prostate for Proscar. These numbers come from separate trials with different people, lengths and methods, so they are not a head-to-head comparison.
Both labels say women who are or may be pregnant should not handle crushed or broken tablets, because finasteride could harm a male fetus.12 Both say finasteride lowers PSA, and that any confirmed rise from the lowest value on treatment is evaluated, even within the normal range. Both carry the high-grade prostate cancer warning from a 7-year trial of finasteride 5 mg a day: Gleason 8-10 cancer in 1.8% vs 1.1% on placebo.12 Reports after approval in both labels include sexual problems that continued after stopping, depression, suicidal thoughts and male breast cancer.12
Which, if either, fits is for your prescriber. More detail: Propecia side effects, Proscar side effects, the Propecia and Proscar dosing schedules, the Propecia and Proscar missed-dose pages, and Finasteride vs dutasteride: how do Propecia and Avodart differ?.