Most Common Side Effect of Testosterone Therapy in Transgender Men
The most common side effect of testosterone therapy in transgender men is acne, particularly during the first 6 months of treatment, with up to 39% developing moderate to severe acne within the first year. 1
Acne as the Primary Dermatologic Side Effect
Testosterone therapy consistently causes increased skin oiliness and acne development in transgender men. The FDA label for testosterone explicitly lists "seborrhea and acne" under skin and appendage adverse reactions 2. Research demonstrates that:
- Moderate to severe acne prevalence increases dramatically from 11.8% at baseline to 39.1% after one year of therapy 1
- Acne severity peaks at 6 months after initiating testosterone, then typically improves with continued treatment 3
- After long-term therapy, most patients (93.9%) have only mild or no acne lesions 3
Risk Factors for Severe Acne
Specific factors increase the likelihood of developing moderate to severe acne 1:
- BMI >25 kg/m² (46% increased risk)
- Age 18-25 years at treatment initiation (98% increased risk)
- Testosterone levels >10 nmol/L (91% increased risk)
- Pre-existing acne at baseline (82% increased risk)
Other Common Side Effects
While acne is most prevalent, the Endocrine Society guidelines outline the expected physical changes within the first 3 months 4:
Early effects (1-3 months):
- Cessation of menses
- Increased libido
- Increased facial and body hair growth
- Increased skin oiliness (precursor to acne)
- Increased muscle mass
- Fat redistribution
Important metabolic considerations:
- Erythrocytosis (elevated red blood cells) occurs in up to 20% of patients and requires monitoring 4, 5
- Transient liver enzyme elevations occur in up to 15% of patients 4
- Changes in lipid profiles (increased triglycerides, decreased HDL cholesterol) 5
Clinical Monitoring Recommendations
The FDA label emphasizes that hemoglobin and hematocrit levels should be checked periodically to detect polycythemia 2. The Endocrine Society guidelines recommend standard monitoring including 4:
- Complete blood counts
- Liver function tests
- Lipid panels
- Blood pressure monitoring
- Weight monitoring
Key Clinical Pitfall
Do not confuse common expected effects with serious adverse events. While acne, increased body hair, and voice changes are expected masculinizing effects, serious complications like erythrocytosis requiring intervention occur in a minority of patients. The distinction matters for counseling: acne is nearly universal and temporary, while polycythemia requires dose adjustment or route change (switching to transdermal administration) 5.
Counsel patients before starting therapy that acne will likely worsen during the first 6 months but typically improves thereafter, and that risk factors like higher BMI and younger age increase severity 1, 3.