Finasteride:

Finasteride is a prescription medication that is FDA-approved for the treatment of androgenic alopecia in men. It works by inhibiting the production of DHT, which is a hormone that plays a role in hair loss. Finasteride inhibits DHT by blocking the enzyme 5-alpha-reductse (type 2) which normally converts testosterone to DHT. The half life of finasteride is 6 to 8 hours meaning the medication is metabolized within a day or two. Finasteride is available in tablet form and should be taken once daily. Most patients tolerate finasteride without side effects. In the first year of therapy roughly 2% of men report decreased libido, erectile dysfunction, and ejaculatory dysfunction. After the first year this drops to less than 1%.

Dutasteride:

Dutasteride is a prescription medication that is FDA-approved for the treatment of androgenic alopecia in men. It works by inhibiting the production of both DHT. Specifically dutasteride inhibits the enzymes 5-alpha-reductase (type I and II). It has a half life of approximately 5 weeks. The combination of a longer half life and inhibition of two types of 5-alpha-reductase enzymes results in significantly more inhibition of DHT than with finasteride. Dutasteride is available in capsule form and should be taken once daily. Side effects are similar to finasteride in that most patients tolerate dutasteride without side effects. Rarely some men report decreased libido, erectile dysfunction, and ejaculatory dysfunction.

Which is more effective, finasteride or dutasteride?

As dutasteride blocks more DHT it should theoretically be more effective. There are a few studies comparing the two and they generally show dutasteride to be more effective in treating androgenic alopecia.