Short answer: Propecia (finasteride 1 mg) is FDA approved for male pattern hair loss. Avodart (dutasteride 0.5 mg) is approved only for an enlarged prostate (BPH), so using it for hair loss is off label.12 Finasteride mainly blocks type II 5α-reductase; dutasteride blocks types 1 and 2. Dutasteride's half-life is about 5 weeks, finasteride's 5 to 6 hours.
| Finasteride (Propecia 1 mg) | Dutasteride (Avodart 0.5 mg) | |
|---|---|---|
| What it blocks | Type II 5α-reductase, with about 100-fold selectivity over type I1 | Both type 1 and type 2 5α-reductase2 |
| FDA-approved use | Male pattern hair loss in men only1 | Symptomatic BPH in men with an enlarged prostate. Not approved for hair loss2 |
| Label dose | 1 mg by mouth once daily, with or without meals1 | 0.5 mg capsule once daily, for BPH2 |
| Half-life | About 5 to 6 hours in men 18 to 60; about 8 hours over 701 | about 35 days (label: about 5 weeks at steady state). Still detectable 4 to 6 months after stopping2 |
| Effect on DHT | Serum DHT down 65% within 24 hours of a 1 mg tablet1 | Median serum DHT down 85% after 1 week and 90% after 2 weeks of 0.5 mg daily2 |
| Effect on PSA | Mean PSA fell from 0.7 to 0.5 ng/mL at 12 months in men aged 18 to 411 | PSA about 50% lower within 3 to 6 months2 |
| Sexual side effects in label trials | First year vs placebo: lower libido 1.8% vs 1.3%, erectile dysfunction 1.3% vs 0.7%1 | Months 0 to 6 vs placebo (BPH trials): impotence 4.7% vs 1.7%, lower libido 3.0% vs 1.4%2 |
| Pregnancy handling | Pregnant women should not handle crushed or broken tablets1 | Pregnant women should not handle capsules; dutasteride can be absorbed through skin2 |
| Blood donation | No rule in the label | Do not donate blood until at least 6 months after the last dose2 |
No, not in the US. The Avodart label lists one use: symptomatic benign prostatic hyperplasia (BPH) in men with an enlarged prostate, alone or with tamsulosin.2 Propecia is the finasteride product approved for male pattern hair loss, and its label says it is not for women or children.1 A prescriber can still write dutasteride off label for hair loss, but the dose and safety data on the label come from older men with BPH, not from hair loss trials.
Yes, in one 24-week randomized trial of 917 men aged 20 to 50. Men took dutasteride 0.02, 0.1 or 0.5 mg, finasteride 1 mg or placebo every day. Dutasteride 0.5 mg increased hair count and hair width in a 2.54 cm circle at week 24 more than finasteride (P=.003 and P=.004) and placebo. The number and severity of side effects were similar across groups. The authors note the study lasted only 24 weeks.3
For finasteride alone, the Propecia label reports a 107-hair difference from placebo in a 1-inch circle at 12 months in men with crown hair loss, and says benefit usually takes three months or more of daily use and reverses within 12 months of stopping.1
Finasteride clears within hours. Dutasteride has a half-life of about 5 weeks, reaches about 90% of its steady level after 3 months of daily use, and stays measurable for 4 to 6 months after the last capsule.2 That long tail is why the Avodart label asks men not to donate blood for 6 months after stopping, so it does not reach a pregnant transfusion recipient.2
Full label numbers: Propecia side effects, Avodart side effects, and the Propecia and Avodart dosing schedules.