I have read on the boards that ATD will lower libido due to its affinity to attach to the androgen receptors, this actually blocking other androgens such as testosterone.
OTOH, I have read (and ALR has claimed) that ATD is site specific in binding to the AR, and its affinity is for the ARs at the hypothalamous. This is why there is no androgen negative feedback, and testosterone levels will continue to rise as ATD, being an AI, lowers estrogen. The only studies I have seen confirming this were done in quail, for what that's worth.
My experience has been a noticeable decrease in libido when taking ATD, even at 25-50 mgs/day.