Cigarettes/Tobacco: Linked to a plethora of types of lung and mouth cancer. Even when you don't smoke it and just "chew" it it can give you mouth cancer. It's bad shit. It completely wrecks your lungs, coating it in tar and a bunch of other nonsense that I don't have time to look up. Highly physically addictive. Helps relieve stress. Alcohol: Can kill you in an afternoon. Causes liver disease/cancer and [i]heavily[/i] impairs the ability to walk, talk, and operate any sort of vehicle, putting those who choose to ignore this impairment at risk as well as everyone around them. Can make people overly aggressive to the point of violence. Kills brain cells. Also possible to become physically addicted. Not known to cure anything in anyone. Socially accepted. Sometimes people say they're better at things when they've got a buzz (writing, bowling, video games, piano, stuff like that). Helps relieve stress Marijuana: Makes you paranoid. Smokeable version is also, in recent studies, linked to (FAR LESS SEVERE) types of lung disease. Kills brain cells. Impairs ability to operate motor vehicles as well and puts people in just as much danger if you choose to ignore your impairment as alcohol. Able to be consumed without smoking and without any sort of repercussions like additional types of disease or cancer. Shown to increase appetite which is a plus for anybody in chemotherapy. Linked to the curing or assisting in curing of several types of cancer (i.e. has medicinal properties, unlike tobacco and alcohol). No known signs of physical dependencies or addictions caused by smoking or other consumption. Any addiction thereof is likely entirely mental in nature. Helps relieve stress. If legalized, would no longer be a gateway drug (and I'll tell you why). When one goes to buy recreational marijuana now, one must buy it illegally (unless one lives in Washington or Colorado). Because one is already buying illegally from a dealer who probably either has on them or has access to more than just pot, it is easy to be offered and coaxed into taking other drugs like meth and harder drugs like acid, cocaine, heroine, etc. where you CAN over-dose on it. I'd posit that marijuana only acts as a gateway drug in its illegal state. Yeah, I think it totally makes sense that Marijuana is the illegal one of the three. /sarcasm.