I've heard of this before in online forums and from a few friends who suffer from Bipolar Disorder, but I've heard the transverse, in that it's one of the only things that really offers them relief. I'm certain it's really more of an individual thing, but if you're worried about the two things I assume you are (that is that they shouldn't be smoking weed and having to be the person who brings that up), maybe you could offer them CBD as an alternative. I've actually read a lot of positive research from using it as a treatment for bipolar disorder and because THC, the active psychoactive compound in marijuana, is either in negligible doses or absent entirely, and should, theoretically, absolve the issue of the episodes being triggered. Just trying to offer some middle-ground help.