I've long been wary of these, since we've found (over and over) that human feeding behavior is protected by multiple, overlapping redundant pathways. We are the descendants of a long line of creatures that have made eating and reproducing their absolute priorities in life, and neither of those behaviors are going to be altered lightly. The animals that can be convinced to voluntarily eat so little that they actually lose weight, just through modifying a single biochemical pathway, are all dead. Our ancestors were the other guys.
By all accounts amphetamines work pretty well. Except for the part where your teeth fall out and everything.