being addicted to weed is the same as a caffeine addiction. your body acclimates to the chemical imbalance in your brain. it's how all addictions work. in caffeines case, it blocks the receptors that your body uses to tell that it's tired, thus you stay up longer. after several months of moderate daily doses, however, your body will start to increase its production of the sleep "signaller" in an effort to get you back to normal. which is why people who rarely drink coffee get more of a buzz.
weed's the same concept, but with dopamine. when you smoke weed, it forces your brain to release more dopamine. after continued use, to balance this, your body will produce less dopamine, as it expects some other portion of dopamine to come from marijuana. depending on how long you've smoked it, how often you smoke it and how much you smoke, you will develop different dependencies. withdrawl symptoms are due to the imbalance of dopamine.
note: there are wild differences between people when considering the amount of caffeine and weed (and cigarettes and crack, etc.) that they can take. it's not a universal constant. so some dude could be trippin on something that just buzzed you.
well, that's what i understand, at least.
