It is addictive Psychologically but not Physically.
How so?
Acetylcholine and Nicotine both are agonists for the nicotinic receptors in our nervous system. This serves a very important function in our body. So if you repeatedly introduce an exogenous agonist such as nicotine into your body, your body will produce less acetylcholine. And if you then try to quit, your mind will not only crave it but your body will
need it. Same with heroin, which is an agonist of Mu receptors in our body.
Marijuana on the other hand is not needed by the body. Your mind can certainly crave it, and if you have Marijuana in easy reach, you can certainly get addicted to it. But it still won't be anything like how it is for heroin or nicotine addicts. The addiction is more akin to gambling or fatty/sugary foods.
