Androstenedione is sometimes sought among
pre-operative (and
non-op, thanks
oakling) female-to-male
transsexuals for the same reason it's sought among bodybuilders: it converts to
testosterone.
Testosterone, when introduced in sufficient quantity to the female body, causes development of male secondary sex characteristics, including voice change, rearrangement of body fat, increased hair growth, and, of course, easier muscle development. Unfortunately for FTMs, it's only available through prescription, and getting that prescription often involves a lot of therapy and hassle. So some transguys turn to supplements, including androstenedione.
Andro, however, doesn't always produce the desirable effects of testosterone, and often causes some of the more damaging ones. Usually the best that anyone with a female body can achieve is increased muscle mass, growth of the clitoris, increased sex drive, and maybe a little scratchiness of the voice. On the other side of the coin, use of andro can lead to acne and increased risk of heart or liver disease.
Since testosterone itself can also increase these risks, one of the things that an FTM's endocrinologist has to check for before he goes on testosterone is whether he has any heart or liver problems. If use of androstenedione has caused these, he might be denied testosterone, which is a Very Bad Thing.
The general consensus in the FTM community is that using andro, especially in high doses, really isn't worth it. The only real benefit is for muscle mass, and the potential risks outweigh that. So most of us just bend to the system and jump through whatever hoops are required to get a prescription for actual testosterone.