I've seen people on psych wards with severe psychosis with their Bipolar Disorder - symptoms which were not present before the use of cannabis. THC is a drug, no two ways about it. Drugs pretty much all have possible side effects - paranoia being one of them. I have also experienced first-hand the depression that can follow cannabis use and this can antagonise Bipolar Disorder (for obvious reasons).

Some will have a good experience, some will have a bad experience. It's risky to say the least.
RB.