You guys who're so sure there aren't any withdrawal symptoms haven't done enough reading. Even though it's not a traditional drug of addiction like a narrcotic, cannabis still binds to nerve receptors and causes a chain of cellular reactions that create a high and other responses. Any substance that changes our neurochemistry, especially when it's been taken regularly, can cause some withdrawal effects when people stop taking it. It's not the same violent, craving-filled withdrawal that happens with drugs like poppy-based narcotics or stimulants, but it's type of withdrawal just the same. You see the same effect with Paxil, other SSRI antidepressants, and various other heart and neurological drugs that work by changing neurochemistry or neurotransmitters in other parts of the body. While the cessation of those drugs won't cause withdrawal in the same way that would happen with traditional drugs of dependence, people certainly can have withdrawal effects when stopping them. Headaches, lack of appetite and trouble sleeping are classic cannabis withdrawal symptoms that people report all the time.

Erowid, one one of the best sources available for unbiased information about cannabis, has a heading on the page I'm linking below called "Withdrawal Symptoms."
Erowid Cannabis (Marijuana) Vault : Effects
birdgirl73 Reviewed by birdgirl73 on . How long till withdrawal effects are noticeable? I used to smoke once every 2 weeks with friends, but since I started buying my own weed, I've smoked every day for the last 3 weeks with a day break in each week. Yesterday I had quite an intense session and visualised myself telling my parents I was a drug addict. I'd like to go on a week break, at least, just to make sure that I can without too much trouble. Have I been smoking long enough to produce ill effects like sweating and insomnia or does that only happen with very heavy users? Rating: 5