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

Finasteride is a widely prescribed and generally well-tolerated medication, but it carries a set of known side effects that every patient should understand before starting therapy. Sexual side effects are the most discussed, but there are other important risks as well — including a 2025 EMA update on mental health. Here's what the clinical data actually shows.

How Common Are Finasteride's Side Effects?

In clinical trials for the 1 mg dose (hair loss), approximately 3.8% of men taking finasteride reported one or more drug-related adverse experiences — versus 2.1% on placebo. Most side effects were sexual in nature. The majority resolved in men who discontinued therapy, and incidence decreased to less than 0.3% by year 5 of continuous use.

For the 5 mg dose (BPH), the side effect profile is similar but somewhat more pronounced. Approximately 3.7% of patients discontinued finasteride 5 mg in the PLESS long-term study due to sexual adverse reactions, versus 2.1% on placebo.

Common Side Effects of Finasteride

These are the side effects reported in at least 1% of patients taking finasteride in clinical trials:

Decreased libido (reduced sex drive): The most commonly reported side effect. Reported by approximately 1.8% of men on finasteride 1 mg vs. 1.3% on placebo.

Erectile dysfunction (impotence): Reported by approximately 1.3% of men on finasteride 1 mg in clinical trials.

Ejaculation disorder (decreased volume): Includes reduced ejaculate volume and less common ejaculation disorders.

Breast enlargement or tenderness (gynecomastia): More common with the 5 mg dose. Men who notice new breast lumps, pain, or nipple discharge should call their doctor immediately as these can rarely indicate male breast cancer.

Skin rash: Mild allergic skin reactions have been reported. More severe reactions (swelling of lips, tongue, throat) indicate a serious allergic reaction requiring emergency care.

Serious Side Effects and Boxed Warning

Finasteride carries a boxed warning from the FDA regarding an increased risk of high-grade prostate cancer. In the Prostate Cancer Prevention Trial, finasteride reduced overall prostate cancer incidence by 25% but was associated with an increased rate of high-grade (Gleason grade 7–10) prostate cancer. The clinical significance of this finding remains debated — many experts believe it reflects detection bias — but it requires informed consent and regular prostate screening.

Other serious reported events (from post-marketing data):

Depression: Reported in post-marketing surveillance. Patients with a history of depression should be monitored.

Suicidal ideation (2025 EMA warning): In 2025, the European Medicines Agency confirmed suicidal thoughts as a possible side effect of finasteride, primarily at the 1 mg dose. The majority of reports involved hair loss patients. Call your doctor immediately if you experience any thoughts of self-harm.

Testicular pain: Rare reports of testicular pain in post-marketing data. Report to your doctor if this occurs.

Male infertility / reduced semen quality: Post-marketing reports of male infertility and poor semen quality. Generally reversible after stopping finasteride. If you plan to father children, discuss with your doctor before starting.

Male breast cancer (rare): Post-marketing reports of male breast cancer in patients taking finasteride 5 mg. Immediately report any breast lumps, pain, or nipple discharge to your doctor.

What Is Post-Finasteride Syndrome?

Post-finasteride syndrome (PFS) refers to persistent sexual, neurological, and psychological side effects that some patients report continuing or developing after stopping finasteride. The FDA updated the Propecia label in 2012 to include reports of persistent sexual dysfunction after discontinuation. The condition is recognized by some medical organizations but remains controversial in the literature. If you experience symptoms after stopping finasteride, report them to your doctor and to the FDA's MedWatch program.

Effect on PSA Test Results

Finasteride reduces PSA (prostate-specific antigen) levels by approximately 50% within 6 months of starting therapy. This means your PSA result will appear artificially low, which could mask early prostate cancer. Make sure every doctor involved in your prostate cancer screening knows you take finasteride so they can correctly interpret PSA values.

When to Call Your Doctor

Contact your healthcare provider right away if you experience:

Any breast lump, pain, or nipple discharge

Depression, anxiety, or thoughts of self-harm

Severe allergic reaction symptoms: swelling of face, lips, tongue, throat; difficulty breathing

Sexual dysfunction that persists after stopping the medication

Urinary symptoms that worsen (for BPH patients)

For information about drug interactions, see: Finasteride Drug Interactions: What to Avoid and What to Tell Your Doctor.

To learn more about finasteride's uses and dosage, see: What Is Finasteride? Uses, Dosage, and What You Need to Know in 2026.