I've heard that cannabis may raise peoples' metabolisms, and I can see that as being true to some extent for some people with regular use. Both my boyfriend and I use cannabis for medicinal purposes and both of us have lost weight while using it. I know of other people who don't gain weight and lose it while still smoking, despite the fact that it can cause you to have an appetite.
Suggestion:
All humans body react different, but Cannabis s. may lower your blood sugar and that's why you get the munchies. I don't think there are studies that show it speeds up your metabolism, but if so…it ain't that bad. 
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cigarette es speed up your metabolic rate so it would make sense that a joint would do the same,most of the smokers i know are quite slim despite the attacks of the munchies
people tend to forget to eat when they are stoned and remember eating because they felt so famished. there are pro's and con's on both sides, but you will loose brain cells whether you want to believe it or not.
my metabolism got higher.