It depends on your weight and how much tolerance you have, but a fatal does could be as little as 2 grams (2000mg) of THC, which is about 100X what it takes to get high. Since marijuana is about 20% THC, and you only actually absorb about half of that when you smoke or injest it, the minimum lethal dose is probably about 20 grams, though some people may be able to tolerate a few times that amount. Fatal marijuana overdoses are rare, about 200 per year in the U.S., but they do happen. Claims that you can injest your body weight are based on articles written by advocates who can't do basic math.
