Side Effects of Dutasteride
Dutasteride is associated with several significant side effects, most notably sexual dysfunction (erectile dysfunction, decreased libido, and ejaculation disorders) and gynecomastia, which occur at rates 2-4% higher than placebo in clinical trials. 1
Common Sexual Side Effects
- Erectile dysfunction (impotence): Occurs in approximately 4.7% of patients during the first 6 months of treatment, with decreasing incidence over time (1.4% at 7-12 months, 1% at 13-18 months, 0.8% at 19-24 months) 1, 2
- Decreased libido: Reported in 3% of patients in the first 6 months, decreasing to 0.3% by 19-24 months 1, 2
- Ejaculation disorders: Including decreased ejaculate volume, occurs in 1.4% of patients initially, decreasing to 0.1% by 19-24 months 1, 2
- Persistence of sexual side effects: Some sexual side effects may continue even after stopping dutasteride treatment 2
Endocrine Side Effects
- Gynecomastia (breast enlargement and tenderness): Occurs in 2.3% of patients in mid-term studies compared to 0.74% in placebo groups, with a relative risk of 3.11 1, 2
- PSA reduction: Dutasteride reduces PSA levels by approximately 50% after 12 months of therapy, which must be considered when screening for prostate cancer 1
Potential Serious Side Effects
- Increased risk of high-grade prostate cancer: Some studies suggest a potential increased risk of high-grade (Gleason 8-10) prostate cancer, although this remains controversial 2, 3
- Rare allergic reactions: Including facial swelling and serious skin reactions 2
- Depressed mood: Has been reported in patients taking dutasteride 2, 3
Effects on Fertility and Reproduction
- Reduced sperm count: Dutasteride reduces total sperm count, semen volume, and sperm motility 2
- Fetal risk: Pregnant women should not handle dutasteride capsules due to potential risk to male fetuses 2
- Blood donation restriction: Men taking dutasteride should not donate blood until at least 6 months after their last dose 2
Discontinuation Rates
- Overall discontinuation rate: Approximately 15% in both dutasteride and placebo groups 1
- Discontinuation due to adverse events: Approximately 6-7% in both dutasteride and placebo groups 1
- Most common reason for discontinuation: Impotence (1-1.5%) 1
Time Course of Side Effects
- Highest incidence: Most side effects occur within the first 6 months of treatment 1, 2
- Decreasing incidence: Sexual side effects tend to decrease over time but may remain statistically significant compared to placebo 1
- Long-term use: Studies up to 4 years show no increase in side effects with continued use 4
Clinical Considerations
- Patient counseling: Patients should be informed about potential sexual side effects and their possible persistence even after discontinuation 2, 3
- PSA monitoring: Healthcare providers should account for the PSA-lowering effect of dutasteride when interpreting PSA results for prostate cancer screening 1, 2
- Risk-benefit assessment: Benefits in BPH symptom relief, reduced risk of acute urinary retention (from 5.6% to 3.3%), and reduced need for surgical intervention (from 3.3% to 1.7%) should be weighed against potential side effects 1
Comparison with Other Medications
- Alpha blockers: When compared to alpha blockers for BPH treatment, dutasteride has fewer incidences of dizziness and postural hypotension but more sexual side effects 1
- Finasteride: Dutasteride inhibits both type 1 and type 2 5α-reductase isoenzymes (versus only type 2 for finasteride), resulting in greater DHT suppression (>90% vs approximately 70%) 5, 6