It's a half truth. I have just finished answering a question from someone who had a psychosis after smoking pot for a few years, and there are lots like her. Marijuana can interfere with your thinking and memory and it has a lot more of the cancer producing tars than you find in tobacco (we are starting to see people who have smoking-related cancer who don't smoke tobacco, only marijuana).

I said it is a half truth that marijuana doesn't have bad side effects. It is true that, compared to drugs like heroin or "ice" it causes lot less problems. But to kid yourself that it is safe is just not true: it is a risky business, and the risks grow fast as you use more, which is what usually happens because one of the early side effects is that you develop tolerance (that means you need more to feel it working, which is because it is an addictive drug).

Not using is risk free...except for the risk of not seeming cool or the chance of losing a friend if you don't do what they do.