My sample is probably too small to be significant, but I have known several adults who were often drunk as teenagers. All seemed to have reduced mental abilities. It is possible that they drank as a result of already being below the average level of intelligence? Alternatively could excess alcohol consumption during teenage years has an adverse effect on the development of cognitive functions? Have there been any studies of teenage alcohol abuse? I have known some folks who became alcoholic when they were adults & did not seem cognitively dysfunctional when sober.