Ok, cocaine first. IT causes some changes in the brain that keep one wanting to take it. It can cause progressive damage to the heart and heart failure. The damage, like knife and gun wounds are only when it happens and not later when not getting injured. Like other injuries there is some healing and maybe the injuries get all better and maybe they don t and it is mainly how bad the injury was. If nothing much happened from the injury (and you would know it if you had a lot of heart damage), then there isn t much healing needed and if you don t get injured again, then you are ok. I hate to say marijuana (which doesn t kill people) is worse than cocaine (which kills most people my age who use it.. I am old enough to be your GRANDFATHER), but: 1) the lung effects of smoking anything add up. Everyone who smokes tobacco gets lung injury. A small amount of those who smoke marijuana get some lung reactivity but the damage is less with marijuana. Irritation goes away promptly when one stops smoking. Damage stays but it is basically not possible to have much damage from smoking with under 10 years of use. 2) the brain effects of marijuana are a serious concern when used by people under 21. There is loss of intelligence and this might not come back. There are also changes in the brain that make someone more prone to addictions from marijuana, and this also might not reverse.