and the leaves. it metabolizes in the body rather quickly when ingested. thats why you have to eat a large amount to feel the effects. when you heat it up, you are releasing the molecules of thc into a gas that is not metabolized by the body very efficiently. think about it like this. you can cook a roast in a lot of beer, and not feel the effect when you eat the roast and drink the remaining beer. it changes the chemical composition so the body metabolizes it differently. however if you drink the same amount of uncooked alcohol, you will feel the effects. very similar with cannabis, except in reverse.
p.s. alcohol is one of very very few "nutrients" to be absorbed by the stomach. everything else is absorbed in the small intestine.
p.s.s. my major is nutrition