Finasteride 1 mg and Testosterone replacement therapy (Testogel, Tostran, Testavan)
ASK PRESCRIBER
ASK PRESCRIBER: combining finasteride with testosterone replacement therapy (TRT) is a deliberate clinical strategy in some hair-loss cases on TRT, because TRT can accelerate androgenetic alopecia by increasing the substrate for 5-alpha-reductase to convert into DHT.
Mechanism
Exogenous testosterone raises serum testosterone, which is then converted to DHT by 5-alpha-reductase. In genetically susceptible men, this can accelerate pattern hair loss. Adding finasteride blocks the conversion. The combination is pharmacologically rational but should be a deliberate clinical decision with monitoring of both hormonal markers and any 5-alpha-reductase-inhibitor side effects (psychiatric, sexual).
Practical advice
Discuss with your TRT prescriber and your hair-loss prescriber. The two clinicians should ideally be in correspondence. Monitoring includes total testosterone, SHBG, DHT (for context only, serum DHT correlates poorly with AGA severity), and any side effects of finasteride per the MHRA April 2024 and May 2026 Drug Safety Updates.