Finpecia Does Not Cause Cancer Sores in the Mouth
Finpecia (finasteride) is not associated with oral cancer sores or mouth ulcers based on extensive clinical trial data and guideline reviews. The documented side effects of finasteride are primarily sexual, hormonal, and dermatologic—not oral mucosal.
Documented Side Effects of Finasteride
The comprehensive ASCO/AUA guidelines and multiple large-scale trials have thoroughly characterized finasteride's adverse effect profile, and oral lesions are notably absent 1:
Sexual Side Effects (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 2
- Decreased libido affects 2-4% more patients than placebo, with rates of 3.4-10% in treatment groups 2
- Reduced ejaculate volume is reported in 1.5-7.2% of patients, representing a 2.6-fold increased risk versus placebo 2
- These sexual side effects are reversible upon discontinuation and often decrease over time even with continued use 1
Hormonal/Endocrine Effects
- Gynecomastia (breast enlargement) occurs in 0.5-2.2% of patients versus 0.1-1.1% with placebo 2
- Breast tenderness affects 0.4-0.7% of patients 2
Dermatologic Effects (Topical Formulations Only)
- When topical finasteride is used, localized side effects include scalp pruritus, burning sensation, irritation, contact dermatitis, and erythema 3
- These are application-site reactions, not systemic mucosal effects 3
What the Evidence Shows About Safety
The PCPT trial, which enrolled over 18,000 men and represents the largest and most rigorous evaluation of finasteride safety, found that overall discontinuation rates due to adverse events were approximately 6-7% in both finasteride and placebo groups 1. No oral mucosal lesions, mouth sores, or cancer sores were reported as adverse events 1.
Multiple studies in Japanese populations (3,177 men), European populations (458 men), and comparative trials have consistently failed to identify oral lesions as a side effect 4, 5, 6.
Important Clinical Caveats
- 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 2
- Laboratory monitoring is essential: PSA levels must be doubled after 12 months of therapy to accurately interpret prostate cancer screening, as finasteride reduces PSA by 50% 1, 2
- Overall discontinuation rates are approximately 15% for both finasteride and placebo groups, indicating the drug is generally well-tolerated 2
Conclusion for Clinical Practice
If a patient on Finpecia develops oral ulcers or mouth sores, alternative etiologies should be investigated rather than attributing them to finasteride. Consider autoimmune conditions (aphthous ulcers, Behçet's disease, lupus), nutritional deficiencies (B12, folate, iron), viral infections (HSV, CMV), or other medications the patient may be taking 1.