I was a daily pot smoker for about three years (ages 15-18). My consumption gradually decreased over the next four years until I stopped completely. I couldn't say if pot was responsible for any cognitive impairment. I do have a poorer memory than most of my peers. I'd be quicker to blame my poor memory on the multiple concussions I've had over the years than on my pot consumption. Marijuana exacerbated my very introverted personality. It's possible my social development was crippled to some degree. I'm not good with the people.

I do know a few individuals who have smoked pot regularly for decades. I don't see cannabis having had any negative effects on them or their families. They are intelligent, successful people in long term stable relationships.

I smoked every day for years, quit ages ago. I don't feel any permanent impairment at all.

Having known a lot of older daily smokers (decades) and older alcoholics, alcohol is a lot more damaging, both mentally and physically. I've never seen anyone die in their 40s from marijuana, but I've seen a few people eventually lose that battle with their liver or their kidneys from alcohol. Older alcoholics can be almost shockingingly stupid, too - far worse than young alcoholics.