TL;DR: Answers to the most common questions about dutasteride, covering how it works, safety, dosage, and how it compares to finasteride. All answers reference peer-reviewed clinical data.
General Questions
What is dutasteride used for?
Dutasteride is FDA-approved for bph/">benign prostatic hyperplasia (BPH / enlarged prostate) at 0.5 mg/day. It is also widely prescribed off-label for androgenetic alopecia (male and female pattern hair loss).
How does dutasteride work?
Dutasteride inhibits both type I and type II 5-alpha reductase enzymes, blocking up to 94% of DHT (dihydrotestosterone) production. DHT is the hormone responsible for prostate enlargement and hair follicle miniaturisation.
How long does dutasteride take to work?
For BPH symptom relief, most men notice improvement within 3–6 months. For hair loss, visible regrowth typically requires 6–12 months of consistent use.
Dutasteride vs Finasteride
Is dutasteride stronger than finasteride?
On DHT suppression, yes. Dutasteride 0.5 mg daily reduced median serum DHT by 94% at one year (Avodart label, section 12.2), while finasteride 1 mg daily, the dose used for hair loss, suppresses serum DHT by about 65% (PROPECIA label, section 12.2) and finasteride 5 mg daily by about 70% (PROSCAR label, section 12.2). Dutasteride blocks both the type I and type II isoforms of 5α-reductase; finasteride blocks only type II. At the doses actually used for hair loss, a 24-week randomised comparison found dutasteride 0.5 mg raised total hair count per cm² from 223 to 246, while finasteride 1 mg moved it from 227 to 231 (Shanshanwal and Dhurat, 2017).
Can you switch from finasteride to dutasteride?
Yes. Clinicians do switch patients who plateau on finasteride to dutasteride. Neither the Avodart label nor the finasteride labels describe a washout requirement for the switch, so the timing is a clinical judgement. Discuss it with your prescribing doctor.
Safety & Side Effects
What are the main side effects of dutasteride?
The FDA label pools the three placebo-controlled BPH trials and reports the reactions that occurred in at least 1% of men on dutasteride and more often than on placebo. In the first six months those were impotence (4.7% on dutasteride vs 1.7% on placebo), decreased libido (3.0% vs 1.4%), ejaculation disorders (1.4% vs 0.5%) and breast tenderness or enlargement (0.5% vs 0.2%). The label shows each of these falling over months 7 to 24, so the sexual effects cluster early in treatment. The other large dataset is the REDUCE trial, which randomised 8,231 men aged 50 to 75 for up to four years and is the source of the label’s high-grade prostate cancer signal (Gleason 8-10 in 1.0% on dutasteride versus 0.5% on placebo).
Does dutasteride cause permanent side effects?
For most men they are transient. The current Avodart label is explicit on the open question: it footnotes the sexual adverse reactions with the statement that they “may persist after treatment discontinuation” and that “the role of dutasteride in this persistence is unknown”. A subset of users report persistent symptoms, discussed as Post-Finasteride or Post-5ARI Syndrome, and the mechanism and true incidence remain under investigation.
Is dutasteride safe for women?
Dutasteride is contraindicated in pregnant women and women of childbearing potential due to risk of fetal harm. It is prescribed off-label for post-menopausal women with pattern hair loss in some countries.
Dosage & Practical Questions
What is the standard dutasteride dose?
The FDA-approved dose for BPH is 0.5 mg once daily (Avodart). For hair loss, 0.5 mg/day is most commonly used off-label, lower daily doses have been studied. A 24-week randomised trial compared 0.05, 0.1, 0.5 and 2.5 mg and found the effect on hair count was dose-dependent (Olsen et al., 2006). Alternate-day dosing is used off-label and is not described in the FDA label.
What happens if I miss a dose?
Due to dutasteride’s long half-life (~5 weeks), a single missed dose has minimal clinical impact. Take the missed dose as soon as you remember unless it is close to your next scheduled dose. Never double up.
Do I need a prescription for dutasteride?
Yes. Dutasteride is a prescription-only medication in the United States. It is available from telehealth platforms, urologists, dermatologists, and GPs who treat hair loss or BPH.
Sources
- FDA. Avodart (dutasteride) prescribing information, NDA 021319. accessdata.fda.gov
- FDA. PROPECIA (finasteride) prescribing information. dailymed.nlm.nih.gov
- FDA. PROSCAR (finasteride) prescribing information. dailymed.nlm.nih.gov
- Shanshanwal SJ, Dhurat RS. Superiority of dutasteride over finasteride in hair regrowth and reversal of miniaturization in men with androgenetic alopecia. Indian J Dermatol Venereol Leprol. 2017 Jan-Feb;83(1):47-54. PMID 27549867
- Olsen EA, Hordinsky M, Whiting D, et al. The importance of dual 5alpha-reductase inhibition in the treatment of male pattern hair loss. J Am Acad Dermatol. 2006 Dec;55(6):1014-23. PMID 17110217