Drugs that affect GABA levels are ones used for anesthesia and anti-seizure medications - because GABA acts to slow you down, calm you down, and put you to sleep. I don't recommend a lifetime of general anesthesia for weight control, but two anti-seizure medications - topiramate and zonisamide - have been shown to cause weight loss.
They work because the drugs calm the nerve activity in your brain that signals you to eat (plus, you can't very well snort down a dozen glazed when you're snoozing head-over-chest on the recliner). Topiramate, in fact, is a method of choice for some weight-loss docs, but its class of drugs does have potential side effects; they can make you feel disoriented as if you're in a zombie-like state.
Find out more about this book:You, on a Diet: The Owner's Manual for Waist Management