Finasteride and Dutasteride: The Complete Guide to DHT Inhibitors for Hair Loss
Finasteride and dutasteride are the most effective medications against androgenetic alopecia. Yet their mechanism, comparative efficacy, and side effects remain poorly understood. A complete, evidence-based guide.
Why DHT Causes Hair Loss
Androgenetic alopecia is caused by follicle sensitivity to dihydrotestosterone (DHT), derived from testosterone via the enzyme 5-alpha-reductase (5aR). DHT causes progressive miniaturization of genetically sensitive follicles until complete extinction. 5aR inhibitors block this conversion and reduce scalp DHT levels.
Finasteride (Propecia): Mechanism and Efficacy
Finasteride 1mg selectively inhibits 5aR type II, responsible for 60-70% of follicular DHT production. It reduces serum DHT by approximately 65-70%.
- Stops or slows hair loss in 83-90% of cases
- Visible regrowth in 60-65% of patients after 2 years
- Optimal results after 12-24 months of continuous treatment
- Most effective on the vertex (crown) and midline frontal zone
FDA-approved since 1997. Prescribed for nearly 30 years with a well-established safety profile.
Dutasteride (Avodart): More Powerful
Dutasteride 0.5mg inhibits both isoforms of 5-alpha-reductase (types I AND II), reducing DHT levels by 90-95% — 25 to 30 percentage points more than finasteride.
- Superior to finasteride in regrowth in direct comparative studies
- Visible results faster (6-9 months vs 12 months)
- Particularly suited for rapidly progressive cases (Norwood IV-VI)
- Much longer half-life (5 weeks vs 6 hours)
Side Effects: Reality vs Perception
Clinical trial data show:
- Erectile dysfunction: 1-2% of patients (vs 0.7% in placebo group)
- Decreased libido: 1-1.5%
- Ejaculatory disorders: 1.2%
Most effects are reversible upon discontinuation. The nocebo effect is well-documented in the scientific literature.
Optimal Protocol
- Finasteride: 1mg/day, oral, at a fixed time
- Dutasteride: 0.5mg/day OR 0.5mg/week depending on profile and tolerance
- Evaluate efficacy at 12 months minimum
- Stopping = progressive relapse within 6-12 months: lifelong treatment
- Annual monitoring recommended (PSA, hormonal panel if needed)
FUE Transplant + DHT Inhibitors: The Complete Strategy
- Finasteride/Dutasteride for miniaturizing zones: stabilizes what remains
- FUE transplant for definitively extinct zones: restores what is lost
Starting an inhibitor before the transplant often stabilizes progression and optimizes surgical planning.
Finasteride, dutasteride, or FUE transplant — which solution is right for your hair loss? Free consultation at Phoenix Hair Center Paris — personalized diagnosis, no commitment.
