Anecdotally, someone I know in the military was deployed overseas somewhere in the 2006-2010 timespan. When I asked what he would appreciate the most, he gave the name of a "weight loss" pill. (I can't remember the name for the life of me.) When I asked why, he said that it keeps everyone alert way better than caffeine.
Also anecdotally, but some of them also will cause a false-positive (or maybe not a true false-positive...but a false-positive in the sense that the soldier didn't intentionally ingest a banned substance) for amphetamines from urinalysis, which is a nightmare for the soldier and their leadership. Jack3d and C4 come to mind right off the bat, and those have since been removed from the GNC on post - or they removed whatever blend that had the compounds causing the false-positive. Every couple of months something new comes on the market that causes the same damn thing and the on-post GNC goes back under the microscope.
It's one of those problems where you know that soldiers are going to buy this stuff no matter how many times you tell them "don't, you don't know what's in it", and they'll get it either online or off-post from places where the command has less influence on what's available.
Anecdotally, someone I know in the military was deployed overseas somewhere in the 2006-2010 timespan. When I asked what he would appreciate the most, he gave the name of a "weight loss" pill. (I can't remember the name for the life of me.) When I asked why, he said that it keeps everyone alert way better than caffeine.