if marijuana is addictive it's on par with caffeine, which is to say not very addictive at all
Just for the record, caffeine is quite addictive, though not dangerously so. You can get withdrawal effects from trying to stop caffeine after regular daily usage, such as nasty headaches and just a general feeling of shittyness and lack of focus (essentially the opposite of its stimulant effect). Fortunately, unlike more dangerous drugs, the withdrawal effects, while really nasty-feeling in the short term, usually last no more than one week (which I found surprising, but it's true) or even as short as a couple days. I was recently (a year or two ago) able to quit caffeine and have avoided it since, and I'm glad I did.
Marijuana on the other hand has no withdrawal nastiness, and so is not chemically addictive in that sense. Any addiction is more out of psychological enjoyment or merely behavioural habit. But you don't get physical withdrawal effects if you stop. So, I think it's fair to say that caffeine is much more addictive than marijuana.