Finasteride (brand name Propecia in 1mg hair loss formulation) is the most extensively studied and most effective medical treatment for male androgenetic alopecia. Understanding how it works, what results to realistically expect, and how to weigh the side effect profile helps patients make informed decisions.
How Finasteride Works
Androgenetic alopecia (male pattern baldness) is driven by dihydrotestosterone (DHT) — a potent androgen derived from testosterone through the enzyme 5-alpha reductase. DHT binds to androgen receptors in hair follicles, progressively miniaturising them until they stop producing visible hair.
Finasteride is a 5-alpha reductase inhibitor. It reduces serum DHT levels by approximately 70% at the standard 1mg daily dose. With DHT significantly reduced, the miniaturisation process slows or stops — allowing follicles that were progressively shrinking to stabilise, and in some patients, partially recover.
What Results to Expect
Stopping loss: Finasteride stops or significantly slows hair loss progression in approximately 83% of men at 12 months. In the remaining 17%, loss continues despite treatment.
Regrowth: Some patients (approximately 66% in the landmark 5-year trial) see modest regrowth — typically in the midscalp and crown. Frontal hairline regrowth is less common and less pronounced.
Timeline: Results begin at 3–6 months but are best assessed at 12 months. Patients who have not responded by 12–18 months are unlikely to respond further.
Indefinite use: The benefit is maintained only while finasteride is taken. Stopping finasteride reverses the DHT suppression — and lost hair begins to shed again within 3–6 months of stopping.
Side Effects: What the Evidence Actually Shows
Finasteride's side effect profile has been extensively studied. The most widely reported potential side effects are sexual side effects: decreased libido, erectile dysfunction, and reduced ejaculate volume.
In the landmark clinical trials, these effects occurred in approximately 1.8% of patients in the finasteride group versus 1.3% in the placebo group. The majority resolved on discontinuation of the medication.
Post-finasteride syndrome: A small number of patients report persistent sexual, cognitive, or emotional symptoms after stopping finasteride — a condition described as post-finasteride syndrome (PFS). The mechanism is not yet fully understood and the condition is actively researched. While rare, it is a legitimate consideration for patients.
Who Should Not Take Finasteride
- Women (especially those who are or may become pregnant — finasteride can cause birth defects in male foetuses)
- Patients with a history of prostate cancer (requires specialist discussion)
- Patients who have had prior adverse reactions to 5-alpha reductase inhibitors
Finasteride and Hair Transplant
Finasteride is commonly used alongside hair transplantation to protect surrounding native hair from progressive loss. A transplant restores hair to bald areas; finasteride reduces ongoing loss in the surrounding native hair.
Considering finasteride? Discuss your individual risk profile with our team or your GP. We provide guidance on medication as part of our comprehensive consultation process.