Finasteride Sexual Side Effects: Lee 2019 Research Summary
This is a plain-language summary of the original published research. We do not add conclusions or opinions of our own. This is not medical advice — consult a certified healthcare practitioner before making any decision.
Original research published in Acta Dermato-Venereologica, 2019
Adverse Sexual Effects of Treatment with Finasteride or Dutasteride for Male Androgenetic Alopecia: A Systematic Review and Meta-analysis
Study conclusion
Men taking finasteride 1mg for pattern hair loss were 66% more likely to report a sexual side effect than men on placebo, and nearly twice as likely to report erectile dysfunction, according to a meta-analysis of 15 controlled trials with 4,495 men. In raw numbers, 5 in every 100 men on finasteride reported a sexual side effect compared to 3 in every 100 on placebo. Reduced sex drive and difficulty ejaculating trended higher with finasteride but did not reach statistical significance on their own.
Strength of evidence
Based on 15 randomised double-blind placebo-controlled trials (the gold standard study design) with 4,495 participants. Results were consistent across studies with very low variation. Score reduced by two points because side effects were measured by self-report only, and most included trials disclosed financial relationships with pharmaceutical companies.
Who it applies to
Who was studied
Adult men with pattern hair loss treated with oral finasteride 1mg per day or oral dutasteride 0.5mg per day. The analysis pooled 1,882 men on finasteride and 375 men on dutasteride, with placebo groups of similar size. Mean ages were comparable across treatment and placebo groups in each trial.
Who was NOT studied
Women were excluded from all included trials. Men using higher finasteride doses (5mg per day, used for prostate enlargement) were excluded, so findings apply only to the 1mg hair loss dose. Men with pre-existing sexual dysfunction, endocrine disorders, or urological diseases were also excluded.
What to look for when shopping
The study measured three specific side effects: erectile dysfunction, reduced sex drive, and difficulty ejaculating. Only 5.31% of finasteride users experienced any sexual side effect versus 3.05% of placebo users. These are the three specific side effects worth discussing with a prescribing doctor before starting.
What research cannot help you decide
The study cannot tell you whether side effects will reverse after stopping finasteride, as most trials did not track recovery after discontinuation. It cannot predict who is at higher individual risk. It also does not address the contested question of post-finasteride syndrome (persistent side effects after stopping).
Key findings
- Men on finasteride 1mg were 66% more likely to report any sexual side effect compared to men on placebo (a statistically significant finding).
- The risk of erectile dysfunction was nearly doubled with finasteride 1mg compared to placebo (also statistically significant).
- In raw numbers: 5 in every 100 men on finasteride reported a sexual side effect, vs 3 in every 100 men on placebo.
- Reduced sex drive trended higher with finasteride but did not reach statistical significance on its own.
- Difficulty ejaculating also trended higher with finasteride but was not statistically significant.
- Dutasteride 0.5mg showed no statistically significant increase in sexual dysfunction, but far fewer trials studied it so the picture is incomplete.
What they did
The researchers searched three major medical databases (MEDLINE, Embase, and the Cochrane Library) for every controlled trial ever published on finasteride 1mg or dutasteride 0.5mg for pattern hair loss, going back to 1946. To be included, a trial had to be double-blind (neither participants nor researchers knew who got the real drug), placebo-controlled, and had to report how many men experienced sexual side effects. Fifteen trials met those criteria, covering 4,495 men in total.
Two independent reviewers extracted the data from each trial and checked each other's work. They then combined all the results mathematically to calculate one overall risk estimate. They used a statistical model designed for situations where different studies have different populations and study lengths, which was the case here.
The results were notably consistent: the variation between studies was essentially zero, which strengthens confidence in the pooled result. The researchers also checked for publication bias (the tendency for positive results to be published more than negative ones) and found it was low. They ran a separate test removing the oldest study population from the analysis and got the same result, confirming the finding was not driven by any single study.
What they found
| Comparison | Result | Significant? |
|---|---|---|
| Finasteride 1mg vs placebo: any sexual dysfunction | 66% more likely to report any sexual side effect (5.31% of finasteride users vs 3.05% on placebo) | Yes |
| Finasteride 1mg vs placebo: erectile dysfunction | Nearly twice as likely to report erectile dysfunction (statistically significant) | Yes |
| Finasteride 1mg vs placebo: decreased libido | 40% more likely to report reduced sex drive, but this did not reach statistical significance | No |
| Finasteride 1mg vs placebo: difficulty ejaculating | 59% more likely to report difficulty ejaculating, but this did not reach statistical significance | No |
| All 5-ARIs vs placebo: any sexual dysfunction | 57% more likely to report any sexual side effect across both drugs combined (statistically significant) | Yes |
| All 5-ARIs vs placebo: decreased libido | 53% more likely to report reduced sex drive across both drugs combined (statistically significant) | Yes |
| Dutasteride 0.5mg vs placebo: any sexual dysfunction | 37% more likely to report any sexual side effect, but this did not reach statistical significance | No |
Limitations
- 1.Most included studies did not describe detailed randomisation, concealment allocation, or blinding methodology, so a low risk of bias cannot be guaranteed.
- 2.Most studies disclosed varying degrees of relationships with pharmaceutical companies.
- 3.Adverse sexual effects were based on patients self-reports only, not objective measurement tools.
- 4.Most studies did not specify the timing of onset of side effects or recovery after stopping the drug.
Who funded it
No funding source was declared for this study. The authors stated no conflicts of interest.
Used in these articles
Links added as fact-checks and articles citing this study are published.