Practically impossible - I'd actually say borderline, as the amount you'd need to smoke is like 500lbs in less than 15 minutes. You'd die from smoke inhalation long before you'd OD. For people saying "every heroin/coke/meth addict started with marijuana" forgets that they also drank milk long before. Does that mean that milk causes people to do any of those things? No, not at all. Correlation =/= causation.