I don't see any way that you can use drugs to lose weight without gaining it back. Are you overweight or are you simply looking to lose a few pounds? If your reason for being overweight is compulsive overeating, then you're one of us lucky ones who looks outside ourselves for happiness or to fill a void, and so you will most likely use drugs in this way. I've been through food binges and I've been through drug binges and I can tell you that no matter what it is that you use, addiction is the exact same thing. If somebody who has no control over their diet or weight tells you that you have no right to use drugs and get high, you can either try to inform them about addiction which will most likely fail, or leave and snicker at the fact that at least your addiction gets you high. But seriously, both of them are horrible and can make your life completely miserable. Please don't use meth for weight loss, find out whats making you overeat in the first place and slowly start a healthy lifestyle that you can maintain forever, as opposed to a crash diet that will not last and will most likely leave you with extra weight when you binge after feeling guilty for not being able to stick to it.
I seem to do a good job of projecting me personal experience and expecting everybody else to be the same...oh well...