There's only three things that's actually harmful about smoking a doobie: 1. Munchies, if you don't exercise, you'll get fat! 2. Becoming a slacker right after you've smoked, I for example have a hard time taking my sorry ass to the gym whenever I've smoked, however, I'm only slacking while I'm high, the day after I'm fully restored again. 3. Smoking anything harms your lungs, however, you can just use a vaporizer to avoid this one. The summery is that it's not really harmful at all, infact, I've read that it's actually helping you fortify your immune system, I for once havn't been sick even once ever since I've started smoking.