5α-Reductase Inhibitors Overview
What Are 5α-Reductase Inhibitors?
Section titled “What Are 5α-Reductase Inhibitors?”5α-Reductase inhibitors (5αRI) are medications that reduce the production of dihydrotestosterone (DHT) by inhibiting the 5α-reductase enzyme. DHT is the more potent active metabolite of testosterone, responsible for several androgenic effects:
- Scalp hair loss (androgenetic alopecia)
- Facial and body hair growth
- Increased sebum production (oily skin/acne)
- Prostate enlargement
Role in HRT
Section titled “Role in HRT”5αRIs are not primary anti-androgens. They do not directly lower testosterone levels — instead, they block the conversion of testosterone to DHT. In transfeminine HRT, 5αRIs are typically used as adjunctive therapy in the following scenarios [1] :
- Persistent scalp hair loss after starting HRT
- Unsatisfactory rate of facial/body hair reduction
- T is in female range but DHT remains elevated
- As a supplement to spironolactone or CPA, not a replacement
What 5αRIs Cannot Do
Section titled “What 5αRIs Cannot Do”- ❌ Cannot lower testosterone levels
- ❌ Cannot replace primary anti-androgens
- ❌ Cannot reverse completed skeletal masculinization
- ❌ Cannot promote breast development
Two Common Medications
Section titled “Two Common Medications”| Feature | Finasteride | Dutasteride |
|---|---|---|
| Target | Type II 5α-reductase only | Type I + Type II 5α-reductase |
| DHT reduction | ~65-70% | ~90-95% |
| Half-life | ~6-8 hours | ~4-5 weeks |
| Onset | Months | Months |
| Evidence level | B | C |
| Cost | Lower (generics available) | Higher |