Finasteride and dutasteride are both 5-alpha reductase inhibitors used to treat male pattern hair loss, but they work differently and produce different results. Finasteride blocks type II 5-alpha reductase and reduces scalp DHT by roughly 70%. Dutasteride blocks both type I and type II isoforms, reducing DHT by over 90%. This article compares the two drugs across every factor that matters for your treatment decision.
Mechanism of Action
How Finasteride Works
Finasteride selectively inhibits type II 5-alpha reductase, the enzyme primarily responsible for converting testosterone to DHT in hair follicles and the prostate. At the standard 1mg dose for hair loss, it reduces serum DHT levels by approximately 70%.
Type II 5-alpha reductase is the dominant isoform in scalp tissue, which is why finasteride is effective despite targeting only one of the two enzyme types.
How Dutasteride Works
Dutasteride inhibits both type I and type II 5-alpha reductase. Type I is found primarily in skin, sebaceous glands, and liver, while type II predominates in hair follicles and prostate. By blocking both isoforms at 0.5mg daily, dutasteride reduces serum DHT by over 90%.
This more complete DHT suppression is the basis for dutasteride's potentially greater efficacy, but it also explains its higher side effect profile.
Head-to-Head Efficacy Comparison
The Pivotal Comparison Trial
The most cited head-to-head study randomized 917 men aged 20 to 50 with androgenetic alopecia to dutasteride 0.5mg, finasteride 1mg, or placebo for 24 weeks.
| Metric | Dutasteride 0.5mg | Finasteride 1mg | Placebo |
|---|---|---|---|
| Mean hair count change (target area) | +109.6 hairs | +75.6 hairs | -32.3 hairs |
| Improvement vs finasteride | +45% more regrowth | Baseline comparator | N/A |
| Physician global assessment (improved) | 38% | 31% | 9% |
Dutasteride produced statistically significantly more hair regrowth than finasteride at the 24-week mark.
Long-Term Data
A Korean study following 712 men for 48 months found:
| Timepoint | Dutasteride Improved | Finasteride Improved |
|---|---|---|
| 12 months | 63% | 56% |
| 24 months | 71% | 62% |
| 36 months | 73% | 65% |
| 48 months | 70% | 61% |
Both drugs maintained efficacy over 4 years, with dutasteride consistently showing a modest advantage of approximately 8 to 12 percentage points.
Side Effect Comparison
Both drugs share the same general category of side effects because they both reduce DHT. However, dutasteride's more aggressive DHT suppression leads to higher reported rates.
Sexual Side Effects
| Side Effect | Finasteride 1mg | Dutasteride 0.5mg |
|---|---|---|
| Decreased libido | 1.8% | 3.0% |
| Erectile dysfunction | 1.3% | 1.7% |
| Ejaculation disorder | 1.2% | 1.5% |
| Any sexual side effect | 3.8% | 5.5% |
The difference is meaningful: dutasteride roughly doubles the libido-related side effect risk compared to finasteride.
Half-Life and Reversibility
This is one of the most important practical differences between the two drugs:
| Property | Finasteride | Dutasteride |
|---|---|---|
| Half-life | 5-6 hours | 4-5 weeks |
| Time to clear system | 1-2 weeks | 4-6 months |
| Side effect reversibility speed | Fast (days to weeks) | Slow (weeks to months) |
Finasteride has a short half-life, meaning it clears your system quickly if you stop taking it. If you experience side effects, they typically resolve within days to weeks of discontinuation.
Dutasteride's half-life is approximately 5 weeks. If you experience side effects, it can take 4 to 6 months for the drug to fully leave your system and for DHT levels to normalize. This extended clearance time is a significant consideration for men concerned about potential side effects.
Other Considerations
- Breast tenderness/gynecomastia: Reported at slightly higher rates with dutasteride (1.3% vs 0.8% for finasteride)
- Blood donation: Men on dutasteride should wait 6 months after stopping before donating blood (versus 1 month for finasteride) due to the longer half-life
- PSA effects: Both drugs reduce PSA levels by approximately 50%, which must be accounted for in prostate cancer screening
FDA Status and Availability
| Factor | Finasteride | Dutasteride |
|---|---|---|
| FDA approved for hair loss | Yes (1997) | No |
| FDA approved for BPH | Yes (5mg as Proscar) | Yes (0.5mg as Avodart) |
| Approved for hair loss elsewhere | Yes (multiple countries) | Yes (South Korea, Japan) |
| Available as generic | Yes (since 2013) | Yes |
| Hair loss use in U.S. | On-label | Off-label |
Dutasteride's off-label status in the U.S. means insurance is unlikely to cover it when prescribed for hair loss. Some physicians prescribe it for BPH symptoms in men who also have hair loss, which may improve coverage.
Cost Comparison
| Option | Monthly Cost (Generic) | Annual Cost |
|---|---|---|
| Finasteride 1mg | $5-$30 | $60-$360 |
| Dutasteride 0.5mg | $15-$50 | $180-$600 |
Finasteride is generally cheaper, especially with discount cards and pharmacy programs. Dutasteride's higher cost reflects its different patent timeline and more limited generic competition.
Switching from Finasteride to Dutasteride
When to Consider Switching
The most common scenario for switching is when finasteride has been used consistently for 12 to 18 months without satisfactory results. Before switching, verify that:
- Adherence has been consistent: Missed doses significantly reduce finasteride's effectiveness. If you have been taking it fewer than 6 days per week, improving adherence may be more effective than changing drugs.
- Expectations are realistic: Finasteride halts loss in 80-90% of men but produces visible regrowth in only 65%. If your hair loss has stopped but regrowth is minimal, the drug is working as expected for many users.
- A physician has confirmed the switch is appropriate: Dutasteride's longer half-life (5 weeks vs 5-6 hours) means it commits you for a longer period.
The Switch Protocol
Most doctors recommend a direct switch: stop finasteride on day 1, start dutasteride 0.5mg on day 2. There is no need for a washout period because both drugs target the same enzyme family. Expect 3 to 6 months before the additional DHT suppression from dutasteride produces visible changes beyond what finasteride was providing.
Combination Use
Some dermatologists prescribe finasteride and dutasteride together at reduced doses, though this approach has limited clinical evidence. The more established combination is dutasteride with minoxidil (40-60% regrowth), which attacks hair loss through two distinct biological pathways.
Regional Prescribing Differences
How doctors approach these two drugs varies significantly by country:
| Region | Finasteride Status | Dutasteride Status | Common First-Line |
|---|---|---|---|
| United States | FDA-approved for hair loss | Off-label | Finasteride |
| South Korea | Approved | Approved for hair loss | Dutasteride (commonly prescribed) |
| Japan | Approved | Approved for hair loss | Both commonly used |
| Europe | Approved | Off-label (most countries) | Finasteride |
| Turkey | Approved | Off-label | Finasteride (often paired with transplant) |
In South Korea and Japan, where dutasteride is approved specifically for androgenetic alopecia, it is frequently prescribed as a first-line treatment. Research from these countries has contributed substantially to the dutasteride hair loss evidence base.
Impact on Hair Transplant Planning
Both drugs play an important role in pre-transplant preparation and post-transplant maintenance. The key question is which one better protects native hair around transplanted grafts.
| Factor | Finasteride | Dutasteride |
|---|---|---|
| Pre-transplant stabilization | Effective at 6-12 months | Effective at 6-12 months |
| DHT suppression for native hair | 70% reduction | 90%+ reduction |
| Interaction with graft survival | None (grafts are DHT-resistant) | None |
| Post-surgery continuation | Recommended indefinitely | Recommended indefinitely |
| Drug clearance if surgery complication | 1-2 weeks | 4-6 months |
For hair transplant candidates at Norwood 4-5 (2,500-4,500 grafts), dutasteride may provide better protection of the native hair in the transition zone between transplanted and non-transplanted areas. However, finasteride's faster clearance makes it safer from a surgical risk management perspective.
Which Should You Choose?
Choose Finasteride If:
- You are starting 5-alpha reductase inhibitor treatment for the first time
- You want FDA-approved therapy with the longest safety track record for hair loss
- You prefer a drug with a short half-life that clears quickly if needed
- Cost is a significant factor
- You are at Norwood 2-3 (800-2,200 grafts equivalent) with mild to moderate loss
Consider Dutasteride If:
- You have taken finasteride for 12 to 18 months with insufficient results
- Your doctor recommends more aggressive DHT suppression
- You are comfortable with the longer half-life and clearance time
- You are at Norwood 4-5 (2,500-4,500 grafts equivalent) and want maximum non-surgical benefit before considering transplant
- You understand and accept the slightly higher side effect profile
Decision Summary by Norwood Stage
| Norwood Stage | Recommended Drug | Rationale |
|---|---|---|
| N2 (800-1,500 grafts) | Finasteride | Early stage, high response rate, minimal risk needed |
| N3 (1,500-2,200 grafts) | Finasteride | Good response expected; add minoxidil if needed |
| N3V (2,000-2,800 grafts) | Finasteride or Dutasteride | Vertex responds well to both; dutasteride if aggressive approach preferred |
| N4 (2,500-3,500 grafts) | Consider dutasteride | Stronger DHT suppression may preserve more native hair pre-transplant |
| N5+ (3,000-7,500 grafts) | Either + transplant | Medication alone insufficient; transplant is primary restoration tool |
The Practical Approach
Most hair loss specialists start patients on finasteride. It is FDA-approved for hair loss, has a 25+ year safety record, is cheaper, and clears the system quickly. If finasteride alone is insufficient after 12 to 18 months, switching to or adding dutasteride becomes a reasonable next step.
For men who need surgical restoration, neither drug alone will be sufficient at advanced stages. At Norwood 5 (3,000-4,500 grafts) through Norwood 7 (5,500-7,500 grafts), a hair transplant (FUE: 7-10 day recovery, 90-95% graft survival) combined with medication provides the most complete outcome.
What About Combining Both Drugs?
Taking finasteride and dutasteride together is not standard practice and adds cost without proportional benefit. Since dutasteride already blocks both 5-alpha reductase isoforms, adding finasteride provides no additional enzyme inhibition. If you are switching from finasteride to dutasteride, it is a replacement, not an addition.
Your Next Step
Before choosing between finasteride and dutasteride, know your Norwood stage. Your stage determines whether medication alone is likely to be sufficient or whether surgical options should also be part of your plan. Get your free AI assessment at myhairline.ai/analyze.
Medical disclaimer: This article is for informational purposes only. Both finasteride and dutasteride are prescription medications. Dutasteride is used off-label for hair loss in the United States. Consult a licensed healthcare provider before starting any hair loss treatment.