Dutasteride
Also known as: Avodart, Dutas
Dual 5-Alpha Reductase Inhibitor | Hair Loss & BPH
Overview
Dutasteride is a potent dual 5-alpha reductase inhibitor that blocks both Type I and Type II isoforms of the enzyme responsible for converting testosterone to dihydrotestosterone (DHT). FDA-approved at 0.5mg daily for benign prostatic hyperplasia (BPH) under the brand name Avodart, it is widely used off-label for the treatment of androgenetic alopecia (male pattern hair loss). By inhibiting both isoforms, dutasteride achieves approximately 90% suppression of serum DHT, compared to roughly 70% with finasteride, which blocks only the Type II isoform. This greater DHT suppression translates to potentially superior hair regrowth outcomes in head-to-head comparisons, though it also carries a somewhat higher risk of DHT-related side effects. Dutasteride has an exceptionally long half-life of approximately 5 weeks, meaning it takes several months to reach steady-state levels and equally long for effects to fully wash out after discontinuation.
Key benefits
- Inhibits both Type I and Type II 5-alpha reductase for more complete DHT suppression
- Reduces serum DHT by approximately 90%, compared to 70% with finasteride
- Head-to-head trials show superior hair count improvements over finasteride at 12 and 24 weeks
- FDA-approved for BPH with well-established long-term safety data
- Extremely long half-life allows for flexible dosing schedules (daily or 3x per week)
- Convenient once-daily oral dosing with no injections required
- Can be combined with minoxidil for enhanced hair loss treatment
Mechanism of action
Dutasteride competitively inhibits both the Type I and Type II isoforms of the enzyme 5-alpha reductase. Type II is the predominant isoform in the prostate and hair follicles, while Type I is found primarily in the skin, sebaceous glands, and liver. By blocking both isoforms, dutasteride suppresses serum DHT levels by approximately 90% at the standard 0.5mg dose, compared to the roughly 70% suppression achieved by finasteride (which blocks only Type II). This near-complete DHT suppression more effectively reduces the androgenic stimulus driving follicular miniaturization in genetically susceptible individuals. The exceptionally long elimination half-life of approximately 5 weeks is due to extensive tissue binding and slow clearance. Serum testosterone may increase modestly (10-20%) as a compensatory response to the pronounced reduction in DHT, though this increase remains within the normal physiological range for most men.
Molecular data
- Type
- Synthetic 4-azasteroid compound (dual 5-alpha reductase inhibitor)
- Half-life
- ~5 weeks (extremely long; active metabolite accumulation over months)
Indications
What the research community uses this compound for, with self-reported effectiveness.
Hair Loss
Prostate Health
Dosing protocols
Common protocols by delivery method. Adjust the curve below to model accumulation in your own cycle.
Delivery method
| Protocol | Dose | Frequency | Duration |
|---|---|---|---|
| — | 0.5mg | Once daily | — |
| — | 0.5mg | 3x per week (e.g., Mon/Wed/Fri) | — |
| — | 0.5mg | Once daily | — |
Safety
Reported adverse effects, contraindications, and what to monitor on cycle.
Common side effects
- Decreased libido (reported in 3-5% of men; somewhat higher incidence than finasteride due to greater DHT suppression)
- Erectile dysfunction (reported in 3-5%; more frequently reported than with finasteride)
- Decreased ejaculate volume (reported in 1-2%)
- Gynecomastia or breast tenderness (reported in approximately 1-2%)
Rare side effects
- Testicular pain or swelling
- Depression or mood changes
- Skin rash, urticaria, or allergic reaction
- Angioedema (swelling of face, lips, or tongue)
- Elevated liver enzymes (very rare)
Contraindications
- Women who are pregnant or may become pregnant (dutasteride is teratogenic and can cause abnormalities of external genitalia in a male fetus; even handling damaged capsules poses a risk due to skin absorption)
- Women who are breastfeeding
- Known hypersensitivity to dutasteride, other 5-alpha reductase inhibitors, or any component of the formulation
- Severe hepatic impairment (dutasteride is extensively metabolized by the liver via CYP3A4)
- Pediatric patients (not indicated for use in children)
- Co-administration with strong CYP3A4 inhibitors (e.g., ritonavir, ketoconazole) may significantly increase dutasteride levels
References
Primary literature and clinical-trial data informing this entry.