Yes, marijuana can be MENTALLY addictive, but it is not physically addictive. But then again, lots of things can be mentally addictive. Prime example today of something that is legal yet seriously addictive? Smart phones. There are many people out there (I'd be willing to say at least half the population with a smart phone) who seem to have an almost pathological need to check their e-mail, latest tweets and whatever else they deem important on the 'net via their smartphones. Take a persons smartphone away who uses it almost continuously and watch them start to jones. "Crackberrys" (Blackberry phones) were the first ones that people showed addictive behaviors with. Now? Just about anyone with an Android or IPhone is lost and twitchy if you take it away from them.
And, like I told you before, there have been serious medical studies out there about addiction and marijuana, and it has been shown that marijuana can help people kick more serious addictions because marijuana in and of itself is NOT physically addictive in any way. Matter of fact, cannabis has been proven to be extremely beneficial in helping people kick opiate and alcohol addictions, so much so that those addictions are approved for medicinal marijuana use.