Common Side Effects of Finasteride and Minoxidil
Finasteride causes sexual side effects (erectile dysfunction, decreased libido, reduced ejaculate volume) in 2-4% more patients than placebo, while minoxidil primarily causes scalp irritation and unwanted hair growth on other body parts. 1
Finasteride Side Effects
Sexual Dysfunction (Most Common)
- Erectile dysfunction occurs in an additional 2-4% of patients compared to placebo, with absolute rates ranging from 4.2% to 15.8% depending on study duration 1
- Decreased libido affects 2-4% more patients than placebo, with rates of 3.4-10% in treatment groups 1
- Reduced ejaculate volume is reported in 1.5-7.2% of patients, representing a 2.6-fold increased risk versus placebo 1
- The magnitude of sexual dysfunction is clinically modest: on a 0-100 scale, finasteride causes a mean difference of only 3.21 points compared to 1.26 points for each year of aging 1
- Sexual side effects decrease over time and remain statistically significant but clinically small after the first year 1
Endocrine Effects
- Gynecomastia (breast enlargement) occurs in 0.5-2.2% of patients versus 0.1-1.1% with placebo 1
- Breast tenderness affects 0.4-0.7% of patients 1
Post-Finasteride Syndrome Controversy
- The FDA amended finasteride labels to warn about persistent symptoms after discontinuation, though this is based on anecdotal patient reports rather than prospective trials 1
- Post-finasteride syndrome remains poorly defined and controversial, with unclear data quality supporting its existence 1, 2
Discontinuation Rates
- Overall discontinuation rates are approximately 15% for both finasteride and placebo groups 1
- Discontinuation specifically due to adverse events is 6-7% in both treatment and placebo groups 1
- Only 3.7% of patients discontinued due to sexual side effects versus 2.1% on placebo 3
- In long-term treatment, lack of efficacy (11%) is a more common reason for stopping than sexual side effects (1%) 4
Important Clinical Caveat: Nocebo Effect
- Informing patients about sexual side effects significantly increases their occurrence: 43.6% reported sexual dysfunction when counseled about side effects versus 15.3% when not informed (p=0.03) 5
- This nocebo phenomenon must be considered when counseling patients, as the burden of suggestion may amplify side effect reporting 5
Minoxidil Side Effects
Local Reactions (Most Common)
- Scalp irritation and itching are the most common side effects due to the alcohol content in topical formulations 6
- Scalp redness or inflammation may occur and warrants discontinuation 6
Hypertrichosis (Unwanted Hair Growth)
- Unwanted facial and body hair growth occurs rarely but is reversible upon discontinuation 6
- Increased body hair was reported in 6.6% of patients using minoxidil alone versus 4% in combination with finasteride (p<0.03) 4
- To minimize unwanted hair growth: limit application to scalp only, wash hands immediately after application, and allow 2-4 hours drying time before bed 6
Cardiovascular Effects
- Chest pain, rapid heartbeat, faintness, or dizziness require immediate discontinuation 6
- Postural hypotension and peripheral edema may occur, particularly at higher doses 7
- Cardiovascular symptoms are dose-dependent, with 5mg daily doses causing more frequent effects than lower doses 7
Other Effects
- Sudden unexplained weight gain or swelling of hands/feet warrants stopping treatment 6
- Changes in hair color and/or texture have been reported in some patients 6
Comparative Safety Profile
When comparing both medications directly:
- Finasteride demonstrates higher efficacy (80% clinical improvement) versus minoxidil (52%) but with sexual side effects 8
- Minoxidil side effects are primarily local (scalp irritation) and cosmetic (hypertrichosis) 4, 8
- Both medications have mild, reversible side effects that resolve upon discontinuation 8
- Laboratory abnormalities are minimal: finasteride decreases PSA by 50% (requiring doubling of values for interpretation) but causes no other clinically significant changes 1, 8
Critical Safety Monitoring
For finasteride:
- PSA levels must be doubled after 12 months of therapy to accurately interpret prostate cancer screening 1
- Delayed cancer diagnosis may occur if PSA adjustment is not performed, potentially leading to worse outcomes 1
For minoxidil: