I think parent's point was primarily that its not "hormone causes weight loss", its "hormone causes changes to innate drive, which change behavior, which causes weight loss". If you did the same things off the drugs that you did on, you would lose similar weight.

Given that, the rational of the original comment makes less sense. A hormone that changed your behavior such that the resulting behavior changes made you happier is far more of an obfuscated ask of modern pharmacology, as there is no behavior change that will reliably fix the problem the same way there is for weight loss (eat less).