Anxiety can make me irritable when I'm anxious but not depressed. And certain spots in the hypomania/mania cycle make me very irritable. I agree with wildflowerchild... the anxiety I'd have from possessing an illegal substance would make me even more anxious than I would be without it. I'm also wary of pot because I'm prone to psychosis, and research has shown that smoking pot can cause or exacerbate psychosis in people at risk.

What about going the therapy route? Continue talking with your therapist, work on relaxation techniques like meditation? Yoga and meditation help me tons. CBT is really good for anxiety.