Mine usually vary between 20-40 minutes. The worst though was about 4 hours long. I got this idea in my head that smoking marijuana would relax me, because I have smoked very crappy marijuana in the past and felt fine and less tense. Well, my sis got me medical marijuana from a friend, and I guess it was too strong for me or something, because about 2 minutes after taking two hits I suddenly felt the worst panic in my life. It was like the dam was released of everything I had worked so hard to hold back and control. I know what a panic attack is and can usually talk myself into relaxing eventually when one suddenly appears...this though, was on a whole other level. I welcomed death at one point. I must have worn myself out eventually because I woke up and felt fine. I dont think pot is bad or anything, but definitely will not go near it until I can help myself more effectively with my anxiety.