Briefing · 19 Oct 2026
Finasteride side effects: what the FDA label actually says, in numbers (2026)
The trial rates, the post-marketing reports, and the 2022 label change, taken straight from the FDA prescribing information. Neither the reassurance of a clinic's landing page nor the alarm of a forum thread: the numbers, with their denominators.
Short answer: in the clinical trials behind finasteride's approval, sexual side effects were reported by 3.8% of men taking it against 2.1% taking a placebo, and 1.2% stopped because of them. Since approval, the FDA has added reports of sexual dysfunction that continued after stopping, and of depression and suicidal thoughts — added to the label in August 2022. Those post-marketing reports are voluntary, so no rate can be calculated from them. Both facts are true at once, and most men take finasteride without incident.
Why this page exists
Search for finasteride side effects and you get two kinds of page: clinic marketing that mentions "rare side effects" in a footnote, and forum threads describing life-changing harm. The FDA's prescribing information sits between them, and it is a public document. What follows is what it says, with the numbers kept next to the groups they came from. The full label is linked at the bottom; you can check every figure yourself in about five minutes.
The trial numbers
These come from the controlled trials of finasteride 1 mg in men with male pattern hair loss:
- In the first year, 3.8% of men on finasteride reported decreased libido, erectile dysfunction or an ejaculation disorder, against 2.1% on placebo. The difference between the two groups is the part attributable to the drug: roughly 1.7 men in every 100.
- 1.2% stopped treatment because of those effects, against 0.9% on placebo.
- They resolved in the men who stopped taking it, and also in most of the men who continued taking it.
- In years two to five of the extension studies, the rates of these effects fell in both groups.
For context on what the drug is doing at the same time: 14% of men on finasteride had further hair loss at one year, against 58% on placebo; by year five that was 35% against 100%.
The post-marketing reports
A drug's label grows after approval, as reports come in from people taking it in the real world. Finasteride's label now records:
- Sexual dysfunction that continued after stopping the drug, including erectile dysfunction, decreased libido and problems with orgasm.
- Depression, and suicidal thoughts and behaviour. The FDA added the suicidality wording in August 2022.
- Breast tenderness and enlargement, testicular pain, and allergic reactions including swelling of the lips and face.
- Male breast cancer, in rare reports.
The honest thing to say about this list is that nobody can turn it into a percentage. Post-marketing reports are submitted voluntarily, from a population of unknown size, and a report is not proof that the drug caused the event. That cuts both ways: it does not establish how common these problems are, and it does not establish that they are not real. What it does mean, practically, is that you should know they exist before you start, and that a change in mood is a reason to contact the prescriber rather than to wait it out.
Three things that are easy to miss
- PSA testing. Finasteride roughly halves the PSA reading used to screen for prostate cancer. If you have a PSA test at any point, the person interpreting it needs to know you take finasteride, or a meaningful result can be read as normal.
- Pregnancy. Finasteride is contraindicated in women who are or may become pregnant, because it can affect the development of a male fetus. Women should not handle crushed or broken tablets. Whole tablets are coated to prevent contact with the active ingredient during normal handling.
- Prostate cancer. In trials of the 5 mg dose in older men, there was a small increase in high-grade prostate cancer. The label states that the significance of that finding for the 1 mg hair-loss dose is not known. Worth raising with a clinician if prostate cancer runs in your family.
What to do with all this
Answer the clinic's questionnaire honestly, particularly the questions about mood and about planning a family — they are there for these reasons. Tell the prescriber if anything changes, and stop and seek advice rather than pushing through a change in mood. Remember the drug only works while you take it: the label states that continued use is needed to keep any benefit, and that stopping reverses the effect within about twelve months. And if you are weighing it up, weigh the 1.7-in-100 trial difference against a condition that is otherwise progressive; that is the actual trade, and it is a personal one.
None of this is a recommendation either way. It is the label, in plain words, so that the decision you make with a clinician is an informed one.
Where to go next
- How to get finasteride online: the process and what it costs.
- Finasteride vs dutasteride: the same warnings, one longer wash-out.
- Cheapest oral finasteride online.
Sources
- FDA, Propecia (finasteride) 1 mg prescribing information, revised July 2022: adverse reaction rates, discontinuation rates, post-marketing reports, PSA, pregnancy and prostate-cancer warnings, and the efficacy figures quoted. accessdata.fda.gov
- Al Saffar et al., "US Food and Drug Administration Warning Regarding Finasteride and Suicidal Ideation", European Urology Open Science, 2023: the August 2022 label addition. pmc.ncbi.nlm.nih.gov
This briefing summarises a regulator's published document. It is not medical advice: finasteride is a prescription medicine, and a licensed clinician decides whether it is right for you. If you are taking finasteride and your mood has changed, contact your prescriber or a doctor.
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