Dutasteride Side Effects: What to Know Before You Start

Dutasteride's side effects are similar to finasteride's — mostly sexual, such as reduced libido or erectile and ejaculatory issues, in a minority of men. But because dutasteride blocks DHT more completely and lingers in the body far longer, those effects can be more pronounced and slower to clear. It's prescription-only and used off-label for hair loss.

What dutasteride is

Dutasteride is a dual 5-alpha-reductase inhibitor — it blocks both the type I and type II forms of the enzyme, reducing DHT by roughly 90% or more, compared with about 70% for finasteride, which only blocks type II. It's FDA-approved for enlarged prostate and used off-label, more potently, for hair loss.

Common side effects

Reported by a minority in trials and often reversible, the most common include:

• Reduced libido
• Erectile difficulty
• Decreased ejaculate volume
• Breast tenderness or enlargement (gynecomastia)
• Mood changes in some users

Less common and worth flagging

• Persistent symptoms after stopping have been reported for 5-alpha-reductase inhibitors generally; the phenomenon is not well understood
• Dutasteride lowers PSA — tell any doctor screening you for prostate cancer so results are interpreted correctly
• It should not be handled by anyone who is or may become pregnant, as it can be absorbed through the skin

Should you be worried?

Most men tolerate dutasteride well, and it's typically considered when finasteride hasn't done enough rather than as a first move. The right approach is to discuss your personal risk with a clinician and start only under supervision — especially given how long the drug stays active.