All items, not just marijuana can be addictive when the person using such items is weak minded and incapable of self control. Marijuana simply exhibits an effect in the human brain that some will naturally get addicted to because of how it makes them feel. It is essentially why people get addicted to tobacco, just marijuana is portrayed as an evil entity without justification.
Since marijuana has a relaxing effect on the body, some people may become addicted to the feeling that the herb provides. However, marijuana is not as addictive as drugs like cocaine or heroine, where the body goes through an intense withdrawal process when a person is trying to stop taking the drug. Withdrawal symptoms from marijuana are usually not severe, but people can still become dependent on the drug, especially if they are under extreme stress.
Marijuana is addicting, but not in the sense that most people would assume. It is not like other drugs, such as cocaine or heroin. It does not have chemicals in it that make the body crave it. It's the feeling of being high that people become addicted to, and they rely on it to get through everyday.
Marijuana is not addicting in the sense that it makes you crave more of it. Cigarettes are addicting because even when you want to quit smoking you still crave another cigarette because of your body's dependence on nicotine. I don't believe people who smoke marijuana experience that same type of addiction. If they don't like smoking marijuana they can easily quit.
Generations of Americans have smoked and enjoyed mj now, for at least the past 6 decades. Experience has shown that persons of any ages can use -- by smoking or including marijuana in a favorite recipe -- this substance without any fear of becoming physically dependent on it. Most people who use mj do not go on to become dependent on stronger drugs, so mj it not what some call a "gateway drug." It does happen that a small percentage of individuals go on to abuse other drugs, but mj does not deserve the responsibility for that.