I've been smoking for exactly one year, but my tolerance took a hit after my freshman year of college. I would smoke at least once every day - often 2 or 3 times. I still managed to keep a 3.6 GPA, so I feel good about defeating that stereotype. Anyways, my true high lasts about 1-1.5 hours, but I still feel the effects after the 3rd or 4th hour.