if your going to get put under- smoking weed could react badly with the anestesia. stop smoking weed at least 24hrs before surgery(smoke all you want after!=]). cigarettes are obviously bad no matter what, ( i still smoke em tho) , nicotiene affectsthe central nervous system and having nicotiene in your system may present a similiar issue as bud, when they put you out. 24hrs is pretty much the rule as i understand, same as they tell you not to eat or drink at least 12hrs before surgery for reasons pertaining to the anesthetic. i am just an emt, and my only expiriences with surgery are as a patient; where i smoked bud the day of my surgery and a cigarette right before i went in- and it went fine, but apparently there are risks involved.