I think it depends on the individual's ability to keep his mind at an equilibrium. Honestly, I wouldn't tell anyone who has underlying mental problems NOT to smoke weed, because everybody's symptoms are different and weed affects them differently as well. I've seen it help treat PTSD tremendously and I've seen it help in some people who had Psychosis(mainly high CBD strains/oils)
Well I am diagnosed Bipolar, so "understanding my issues" isn't going to make them go away. I smoke marijuana because it helps me more than the hundreds of different medications I've been on ever have.
I was told not to smoke whilst on anti depressants but not listening to that psychiatrist was probs the best thing I've ever done lol. Felt so much better and even came off my meds HoLLa