While alcohol and acetaminophen aren't metabolized by the same enzyme alcohol does increase the risk of liver damage from tylenol. Just as an honest FYI, watch out when taking medications containing it if you plan on drinking, it can kill you. Drinking water does help a hangover; drinking it after you've finished drinking alcohol is no less helpful than drinking it before and probably even more helpful. Aclohol works as a diuretic, it forces you to urinate much more than you normally would which results in the dehydration. Also build up of lactic acids contributes to the hangover. That's where most of the symptoms come from, dry mouth, head ache, nausea and what not. The only benefit marijuana would provide would be from the immediate effects of the "high". If you'd smoked a bowl yesterday it's not going to help your hangover today.