While Propecia (Finasteride is the generic form) has been approved by the FDA as the only oral treatment for slowing, stopping, and/or reversing hairloss, Avodart (Dutasteride is the generic form), though not yet FDA approved, has shown significant promise in becoming a much more effective oral treatment in battling hairloss, thinning, and outright balding. So many more guys are finding themselves debating which drug to take, what the differences are between Finasteride and Dutasteride, and what the pros and cons are of incorporating them into your daily regimen.
What are the differences between Finasteride vs. Dutasteride?
Both finasteride and dutasteride seek to reduce DHT (dihydrotestosterone) whose presence seems to be the major cause of male pattern baldness. DHT is the result of an enzyme known as 5α-reductase metabolizing testosterone. Both finasteride and dutasteride act by inhibiting 5α-reductase, which in turn dramatically reduces the amount of DHT present in the scalp. The difference in how each drug goes about inhibiting 5α-reductase is where they differ. There happens to be 2 different types of 5α-reductase enzymes, conveniently known as Type 1 5α-reductase and Type 2 5α-reductase. They are located in different area, and in different amounts, though they each play a critical role in creating DHT through metabolizing testosterone.
As it turns out, the trials of each drug show finasteride inhibits only Type 2 5α-reductase, with little effect on Type 1, whereas dutasteride inhibits Type 2 5α-reductase about 3 times better, as well as Type 5α-reductase at a rate of about 100 times better than finasteride.
Results of a Head to Head trial between Finasteride and Dutasteride
As you would expect from the comparison of their efficacy above, dutasteride has consistently outperformed finasteride in head to head trials.
The trials also tested dosage, since Finasteride is currently approved in 1mg (Propecia) and 5mg (Proscar) doses, whereas Dutasteride is only approved in 0.5mg (Avodart) doses, and the results new hair growth after a 24 week Phase II trial among men ages 21-45 were as follows:
Placebo -32.3 hairs
Finasteride 5mg 75.6 hairs
Dutasteride 0.1 mg 78.5 hairs
Dutasteride 0.5 mg 94.6 hairs
Dutasteride 2.5 mg 109.6 hairs
Adverse Side Effects of Finasteride and Dutasteride
Both dutasteride and finasteride were well tolerated in this phase II study, and no new safety concerns have arisen in any of the phase II and phase III studies of dutasteride given at doses up to 5 mg daily (the 5-mg dose was used in a phase II study for BPH).
There were no significant differences in side effects, serious adverse events, or withdrawals due to adverse events among any of the treatment groups, including placebo. In total, 11 subjects withdrew because of adverse events: 3 were in the placebo group (irritable bowel syndrome and impotency), 7 in the dutasteride 0.1 mg group (decreased libido, malaise and fatigue, mood disorders, skin disorders, injuries caused by trauma, and gastrointestinal- and neurology-related complaints) and 1 in the dutasteride 0.5 mg group (gastrointestinal discomfort and pain).
Decreased libido was noted in:
2 subjects in the placebo group
2 subjects in each of the 0.05-mg and 0.1-mg dutasteride groups
1 subject in the 0.5-mg dutasteride group
9 subjects in the 2.5 mg dutasteride group
3 subjects in the finasteride group
Of the 9 subjects with decreased libido in the 2.5-mg dutasteride group:
4 resolved while receiving therapy
1 resolved within 3 weeks
1 resolved within 8 weeks of stopping drug therapy
1 subject, decreased libido continued after therapy had been stopped and was presumed by the subject to be unrelated to the trial or drug therapy
Duration of Effects
The serum half-life of finasteride is 6 to 8 hours. Dutasteride has a serum half-life of approximately 4 weeks, and this long half-life was evident in the persistent suppression of DHT with the 0.5-mg and 2.5-mg doses after dutasteride treatment was stopped. Because of this long half-life, men being treated with dutasteride should not donate blood until at least 6 months past their last dose to prevent administration to a pregnant female transfusion recipient.