Well most of the time if you ask me I think people lace marijuana either because one, the weed is shit and no one will come back to a guy they just meet that has shit weed so they probably put somethin in there to spice it up and make people think it's good or two, the substance they add in the marijuana is addicting and they are trying to get reliable customers that are fiends. Or if your smokin with friends maybe they just like smokin laced shit or maybe they just wanna see you trip out for laughs.