Family & Friends of Bipolar Support Group
This community is dedicated to parents, siblings, grandparents, other relatives and friends of someone who is Bipolar. The purpose of this community is to help families and friends develop greater patience and understanding, as well as maintain a positive, caring relationships with those diagnosed as Bipolar.

I fall into the camp of it being very individual, when it clearly makes things worse it's a mistake. I wouldn't recommend trying it if you've never tried it before either because it is incredibly variable in strength and content.
People who are bipolar and people who are not bipolar self-medicate, and some self-medicate with pot. Marijuana is addictive, don't believe all that bullshit mumbo-jumbo about "natural remedies" - anything that makes your blood sugar drop like a stone is obviously affecting you in a negative way. (That's where the "munchies" come from in case you didn't know.)
Your boyfriend is avoiding becoming stable, and he's lying to his doctors if he's not telling them that he is smoking dope and screwing with his treatment. And he must ne getting it illegally, and thus committing a crime each time, too, right? I can't see anything good about that, can you?
The only time marijuana has legitimate medical uses is when it is being prescribed by a qualified, licensed medical doctor. Usage for chemo patients, diabetics with eye problems, that sort of thing. That's not your boyfriend's problem.