Finasteride and Erectile Dysfunction
Yes, finasteride can cause erectile dysfunction, with clinical guidelines showing a 2-4% increased risk of erectile dysfunction compared to placebo in randomized controlled trials. 1
Evidence of Sexual Side Effects
Finasteride, a 5-alpha-reductase inhibitor (5-ARI), is associated with several sexual adverse effects:
- Erectile dysfunction (ED): Multiple randomized controlled trials consistently demonstrate increased rates of ED in patients taking finasteride compared to placebo
- Decreased libido: Statistically significant higher rates compared to placebo
- Ejaculatory disorders: Particularly decreased ejaculate volume
- Gynecomastia: Small but consistent increased risk
Statistical Evidence
According to clinical guidelines from the American Society of Clinical Oncology and American Urological Association:
- Virtually all RCTs show a 2-4% increase in reported erectile dysfunction with finasteride compared to placebo 1
- In mid-term studies (1-2 years), ED rates ranged from 0.81% to 15.8% in finasteride groups versus 0.4% to 6.2% in placebo groups 1
- In the long-term Prostate Cancer Prevention Trial (PCPT), 67.4% of finasteride users reported ED compared to 61.5% in the placebo group 1
Mechanism and Severity
Finasteride inhibits the conversion of testosterone to dihydrotestosterone (DHT) by blocking the 5-alpha-reductase enzyme:
- While testosterone is more relevant for central modulation of sexual function, DHT has local effects that may impact erectile function 2
- The magnitude of sexual dysfunction is relatively small compared to natural variability in the population 1
- On a scale of 0-100 (higher score indicating more dysfunction), finasteride increased sexual dysfunction by a mean difference of 3.21 points, compared to 1.26 points for each year of aging 1
Duration of Effects
The persistence of sexual side effects is an area of ongoing concern:
- According to the FDA drug label, sexual dysfunction that continues after discontinuation of treatment has been reported, though these events were reported "rarely" 3
- The sexual dysfunction associated with finasteride typically decreases over time during continued treatment, although it remains statistically significant 1
- Some research suggests the possibility of persistent or even permanent sexual side effects in a subset of patients, though this remains controversial 4
Dose-Related Effects
- For male pattern baldness, finasteride is prescribed at 1mg daily, while BPH treatment uses 5mg daily
- A single study showed that in men over 50, the 1mg dose had similar effects on PSA levels as the 5mg dose 1
- Studies show different rates of ED between BPH treatment (5mg) and male androgenetic alopecia treatment (1mg), with higher rates generally reported in BPH studies 5
Clinical Considerations
Nocebo Effect
An important consideration is the potential for nocebo effect:
- One study found that when patients were specifically counseled about potential sexual side effects, they reported significantly higher rates (43.6%) compared to those not informed (15.3%) 6
- This suggests that patient expectations may influence the reporting of sexual side effects
Counseling Recommendations
When prescribing finasteride:
- Inform patients about the 2-4% increased risk of erectile dysfunction
- Discuss that sexual side effects may decrease over time but could persist in some cases
- Explain that discontinuation rates due to sexual adverse events are approximately 6-7% in clinical trials 1
- Consider the patient's baseline sexual function and other risk factors for ED
- Monitor for sexual dysfunction during follow-up visits
Conclusion
While finasteride is effective for its approved indications, the risk of erectile dysfunction is real but relatively modest in magnitude. The FDA label specifically mentions sexual dysfunction as a potential adverse effect, including ED that may continue after discontinuation of treatment 3. Patients should be properly informed about these risks to make an educated decision about treatment.