Side Effects of Oral Finasteride for Hair Loss
Oral finasteride 1 mg daily for male pattern baldness is generally well-tolerated, with sexual side effects (decreased libido, erectile dysfunction, and reduced ejaculate volume) occurring in approximately 2-4% more patients than placebo, and these effects typically resolve upon discontinuation or may even improve during continued treatment. 1
Sexual Side Effects
The most commonly reported adverse effects are sexual in nature:
Erectile dysfunction occurs in approximately 2-4% more finasteride users compared to placebo 1. In the large PCPT trial, 67.4% of men on finasteride reported erectile dysfunction versus 61.5% on placebo (relative risk 1.10) 2
Decreased libido is reported at similar rates (2-4% above placebo) 1
Reduced ejaculate volume affects a small percentage of users 1, 3
Important context: The magnitude of sexual dysfunction is relatively small—finasteride's effect represents a mean difference of 3.21 points on sexual function scales, compared to 1.26 points for each year of aging 4, 2. Sexual dysfunction associated with finasteride decreases over time, even with continued treatment 1
Breast-Related Effects
Gynecomastia (breast enlargement) occurs in approximately 2-4% of patients taking finasteride versus 0.7-2.8% on placebo 1
Male breast cancer has been reported rarely in postmarketing surveillance, though the relationship to finasteride remains unclear 5
Discontinuation Rates
Overall discontinuation rates due to adverse events are approximately 6-7% in both finasteride and placebo groups, indicating the drug is generally well-tolerated 1, 4
New reports of drug-related sexual adverse events actually decrease with duration of therapy 5
Post-Discontinuation Effects
The FDA label notes that some patients have reported:
Persistent sexual dysfunction (erectile dysfunction, decreased libido, ejaculation disorders) that continued after stopping treatment 5
Orgasm disorders have been reported in postmarketing experience 5
These persistent effects are reported rarely, and their independent relationship to finasteride is uncertain given that most men had comorbid conditions and were taking other medications 5
Other Reported Effects
Hypersensitivity reactions including pruritus, urticaria, and angioedema (rare) 5
Testicular pain and hematospermia (rare) 5
Depression has been reported in postmarketing surveillance 5
Male infertility and poor seminal quality reported rarely, with normalization often occurring after discontinuation 5. The 1 mg dose has inconclusive evidence regarding fertility impact 4
Important Clinical Considerations
PSA suppression: Finasteride reduces PSA levels by approximately 50% after 12 months of therapy, which must be accounted for when screening for prostate cancer 1, 2
Contraindication in pregnancy: Finasteride is absolutely contraindicated in pregnant women due to risk of hypospadias in male fetuses 6
Tolerability profile: In phase III studies, only 7.7% of finasteride recipients versus 7.0% of placebo recipients reported treatment-related adverse events 6
Topical Alternative
For patients concerned about systemic side effects, topical finasteride formulations reduce the risk of systemic adverse effects while maintaining efficacy, with side effects localized to the application site (scalp pruritus, burning, irritation) 7