When my Crohns was at its worst, MJ was very effective at managing my symptoms. I have tried nearly every prescription drug possible and none of them worked half as well as MJ. It was the only thing that relieved pain, nausea, gave me an appetite, helped me sleep, and eased stress during a horrible flare. After losing 50 lbs in a few months, I'm not sure if I would be here today without it. When I consulted my GI about using MJ medicinally, he said that if we were in California he would prescribe it for me.
In terms of its negative/addictive effects, it is impossible to be physically addicted to MJ. You can become mentally addicted to the lifestyle, just as you can with gambling or shopping. However, for people who were suffering like me, the only thing I might have become addicted to was feeling better when I used it.
I used MJ everyday for 4 years while I was in college. At the same time, I always had a job/internship, was the president of several large student organizations, and graduated Cum Laude from a top university. It has no effect on my motivation or mental capacity. I have failed to experience any of its "destructive" qualities.
Health wise, smoking anything is generally not good for you. However, ingesting it or using a vaporizor has almost no negative effects on your health.
I stopped using MJ about a year ago, because my job drug tests. I quit cold-turkey with no difficulty. The only time I ever crave it, is when my symptoms are acting up and I know that it is the only thing that could make me feel better. It has been infinitely easier than quitting cigarettes has been. It was also much easier than quitting the percocets that I was prescribed after my surgery, which I only used for a few weeks.
The point I'm trying to make is that you shouldn't be afraid to try something that has the potential to dramatically ease your suffering and improve your quality of life, just because of its negative stigma, based on a plethora of inaccurate and misleading information.