Dutasteride Side Effects: What to Expect and When to Call Your Doctor

Dutasteride (Avodart) is generally well-tolerated, and many patients take it for years without significant problems. But like all medications, it does have a side effect profile that patients should be aware of before starting treatment. This guide covers the most common and most serious side effects of dutasteride, so you know exactly what to expect and when to seek medical attention.

The Most Common Side Effects of Dutasteride

The most frequently reported side effects of dutasteride are sexual in nature. In clinical trials, these effects were more common than placebo but still affected a minority of patients:

Decreased libido (reduced sex drive): Reported in about 3.3% of dutasteride users vs 1.6% on placebo in the largest BPH trial (6,729 men). Most cases are mild and reversible after stopping the medication.

Erectile dysfunction (ED): Reported in about 9% of dutasteride users vs 5.7% on placebo. ED can range from mild to moderate difficulty with erections.

Ejaculation disorders: Includes decreased semen volume, which is common, and other ejaculatory changes. These effects may persist after stopping the medication.

Breast tenderness or enlargement (gynecomastia): Reported in about 1.9% of users vs 1% on placebo. This occurs because dutasteride alters the ratio of testosterone to estrogen in some men, stimulating breast tissue.

Will These Side Effects Go Away?

For most patients, sexual side effects like decreased libido and ED improve or resolve when dutasteride is stopped. However, because dutasteride has an extremely long half-life of about 4-5 weeks, it can take several months after your last dose before blood levels decline significantly. This means side effects may persist longer after discontinuation compared to finasteride, which clears the body in a matter of days.

A subset of patients report persistent sexual side effects even after stopping dutasteride (sometimes called post-finasteride or post-5ARI syndrome). This is a contested area of medicine — some experts believe the effects are permanent in rare cases, while others question the evidence. Discuss any persistent side effects with your prescriber.

Serious Side Effects and FDA Warnings

1. Increased Risk of High-Grade Prostate Cancer

The FDA added a warning to dutasteride's prescribing information in 2011 based on data from the REDUCE trial, a large, 7-year randomized controlled study. Participants taking dutasteride had a higher rate of high-grade (Gleason 8-10) prostate cancer compared to placebo (1% vs 0.5%). The overall rate of prostate cancer was actually lower in the dutasteride group, but higher-grade tumors were more frequently diagnosed.

This means: dutasteride should not be used specifically to prevent prostate cancer. Regular PSA monitoring and prostate cancer screening are essential during treatment. Importantly, dutasteride suppresses PSA by about 50% — your doctor must account for this when interpreting your PSA results.

2. Severe Allergic Reactions

Rare but serious allergic reactions can occur, including angioedema (swelling under the skin, especially of the face, lips, tongue, and throat), urticaria (hives), and rash. Stop taking dutasteride immediately and seek emergency medical attention if you experience:

Sudden swelling of the face, lips, tongue, or throat

Difficulty breathing or swallowing

Severe rash, skin peeling, or blistering

3. Fetal Harm (For Women and Partners)

Dutasteride can cause birth defects in male fetuses if a pregnant woman is exposed to it through skin contact or blood transfusion. Pregnant women or those who may become pregnant must not handle dutasteride capsules. If a capsule leaks and comes into contact with skin, wash immediately with soap and water. Men taking dutasteride must also not donate blood during treatment or for 6 months after stopping.

4. Mood and Mental Health Effects

Some patients report mood changes, depression, and anxiety while taking dutasteride or after stopping it. The relationship between 5-alpha reductase inhibitors and mental health effects is an active area of research. A 2025 study noted reports of depression and suicide associated with oral finasteride — a closely related drug — though causality is not clearly established. If you experience significant mood changes, discuss them with your prescriber.

When to Call Your Doctor About Dutasteride Side Effects

Persistent or worsening ED, decreased libido, or ejaculation changes that are affecting your quality of life.

Breast enlargement, pain, or lumps (any breast lump in a man on dutasteride should be evaluated promptly).

Any signs of allergic reaction — rash, hives, swelling, difficulty breathing.

Significant mood changes, depression, or anxiety — especially if new or worsening.

Worsening urinary symptoms, new pain, or blood in urine while taking dutasteride.

The Bottom Line

Most patients who take dutasteride do not experience serious side effects. The most common issues — decreased libido and ED — affect a minority of users and often resolve with time. Being informed is the best preparation. For a related guide, see our article on dutasteride drug interactions: what to avoid. And if you're having trouble finding your dutasteride prescription, medfinder can help.