Ronald Reagan used to say marijuana kills brain cells. He was wrong. The study back in the 70s he based that on was flawed. The researcher strapped monkeys into chairs, put gas masks on their faces and pumped in the smoke so strong and for so long that animals got brain damage from the lack of oxygen. So, this Dr. Heath, the scientist who did the study, was he really that incompetent? I don't think so. He knew that the US government would only allow and pay for studies that told them what they wanted to hear - that marijuana was bad in some way - so he rigged the study. He purposely brain-damaged those animals to get his funding.
Oh, by the way. Alcohol, if over-used, *DOES* cause brain damage.