Finasteride side effects

Finasteride is the most studied prescription for male pattern hair loss, and in its trials most men had no side effects at all. The label also lists serious problems reported after approval, including depression, suicidal thoughts and sexual side effects that continued after men stopped the drug. Both halves of that picture matter when you decide whether to take it.

Here is what the label and trials say, effect by effect, and what to watch for once you start.

Sexual side effects in the trials

The label’s first-year data come from 945 men on finasteride 1 mg and 934 on placebo. These are the drug-related effects reported more often on finasteride:

Each effect was rare, and each was more common on finasteride than on placebo by less than a percentage point. In other words, for every 1,000 men taking finasteride for a year, the trials suggest roughly 5 to 6 more will have each problem than if they had taken a placebo.

In a 12-month study of 450 men comparing finasteride, minoxidil and both, side effects were reported in 1.8% of the finasteride group and went away after the drug was stopped.

The sexual function questionnaire

In the two crown-loss trials, men also filled in a sexual function questionnaire. At 12 months, results favored placebo in 3 of 4 areas: sexual interest, erections and perception of sexual problems. There was no difference in overall satisfaction with sex life. The label also notes that finasteride did not appear to affect body hair outside the scalp.

Reports since approval

Clinical trials are too small and short to catch rare problems, so the label also lists postmarketing reports: problems doctors and patients reported after the drug went on sale. For finasteride these include:

• Depression, and suicidal ideation and behavior
• Sexual dysfunction that continued after stopping, covering erectile, libido, ejaculation and orgasm disorders
• Male infertility and poor semen quality, which the label says has improved or normalized after stopping in some reports
• Male breast cancer, which the patient information lists as rare
• Testicular pain, blood in the semen, breast tenderness or enlargement, and allergic reactions such as rash, hives and swelling of the lips, tongue, throat or face

Postmarketing reports show that a problem has been reported, not how often it happens or that the drug caused it in every case; the label says as much. They are still part of the FDA-approved label, and the mood and persistent sexual reports are the ones most worth discussing before you start. Some people describe a cluster of lasting symptoms after stopping as “post-finasteride syndrome”; the label does not use that term, but the persistent sexual effects it lists are the core of it.

Mood changes

Tell the clinician who prescribes finasteride about any history of depression or anxiety before you start. Once you are on it, contact them promptly about low mood, loss of interest, or any thoughts of self-harm. These are rare, but the label lists them, and they are the reason a clinician should review your history rather than an automated form alone.

PSA and prostate cancer

Finasteride lowers PSA, the blood test used to screen for prostate cancer. The label says any confirmed rise in PSA from its lowest point on finasteride may signal prostate cancer and should be checked, even if the number is still in the normal range. If you have PSA tests, tell the doctor who orders them that you take finasteride.

The label also says 5-alpha reductase inhibitors may increase the risk of high-grade prostate cancer. The figures behind that warning (1.8% vs 1.1% on placebo for the most aggressive grade) come from a trial of finasteride 5 mg, the prostate dose, not the 1 mg hair loss dose. Dutasteride carries the same warning.

Pregnancy and handling tablets

Finasteride is approved for men only. Women who are or may be pregnant should not handle crushed or broken tablets, because finasteride can affect the development of a male fetus. Intact, coated tablets prevent contact during normal handling.

That risk is larger with topical products, which have no coating. The FDA’s April 2025 alert warned that compounded topical finasteride can transfer to others, especially women, through skin contact.

Who should not take it

The label lists two contraindications: pregnancy, because finasteride may cause abnormalities of the external genitals of a male fetus, and allergy to any ingredient. It is also not indicated for women or children. In a 12-month study of 137 postmenopausal women, finasteride showed no improvement in hair over placebo.

Men with a history of depression, men planning to conceive, and men who have regular PSA tests can still take finasteride, but each is a reason to talk it through with the prescriber first.

Topical finasteride side effects

Topical finasteride is applied to the scalp so less of the drug reaches the rest of the body. In a 24-week European trial of 458 men, a 0.25% spray produced blood finasteride levels more than 100 times lower than the tablet and cut DHT by 34.5% against 55.6%, and side effects were similar to placebo.

The products sold online in the US are different: they are compounded, not FDA-approved, and were not part of that trial. The FDA’s alert reported:

See topical vs oral finasteride for how the two compare on results and cost.

What to do if you notice a side effect

• Tell your prescriber. Online providers such as Hims and Strut Health include messaging and follow-ups in the price; use them.
• Don’t wait out a mood change. Contact a clinician the same day for thoughts of self-harm, or call or text 988 in the US.
• Report it. The FDA asks patients and clinicians to report side effects to MedWatch.
• Know what stopping means. The label says the hair benefit reverses within 12 months of stopping, so weigh that with your clinician, alongside alternatives such as minoxidil.

Weighing the risk

Finasteride’s benefits are well documented: in the label trials, 14% of men on it had further hair loss at 12 months against 58% on placebo, and 35% against 100% at 5 years. Side effects were uncommon in those trials. The rare, serious reports since approval are why the decision deserves a real conversation with a clinician, not a checkbox.

If you decide to go ahead, compare providers by price and follow-up care on our cheapest finasteride list, read how an online prescription works in our finasteride online guide, and see the full label summary on the oral finasteride page or our hair loss hub.