Copied from the Las Vegas meeting notes:
Both finasteride and dutasteride inhibit the development of the type 2 alpha reductase that plays a critical role in the creation of the hair loss causing hormone DHT, only dutasteride also effectively inhibits the development of the type 1 alpha reductase that also plays a role in creating DHT.
According to Dr. Bernie Nusbaum, who presented an update on Dutasteride therapy at the meeting, dutasteride is three times more potent than finateride at inhibiting the type 2 enzyme and 300 times more potent than finasteride in inhibiting the type 1 enzyme.
Based on a randomized, placebo controlled study of 416 male hair loss sufferers, dutasteride improved hair growth in these men more rapidly and to a greater degree than finasteride.
However, dutasteride was shown to remain in the body far longer than finasteride after being discontinued. Dutasteride was also found to reduce sperm counts more dramatically than finasteride along with a higher incidence of decreased libido (13%).
Of additional concern, dutasteride, unlike finasteride, reduces the type 1 enzyme which is found in the brain ??“ unlike the type 2 enzyme which is not present in the brain. Apparently it is not clear at this time what role the type 1 enzyme may or may not play in the functioning of the brain. Thus dutasteride could potentially have yet unknown side effects due to reducing the type 2 enzyme in the brain.