At its absolute worst, it may, potentially, be as harmful as alcohol, but only provided a number of additional provisions. On its own, water has a worse list of side effects, and far more fatalities due to overindulgence. Cannabis has zero fatalities, in and of itself. That isn't to say that it is completely safe to mix with certain prescription drugs, however the incident rate is really quite low. The worst that is likely to happen is that you'll get a gnarly case of the munchies, maybe get the spins, and then pass out. Alcohol can kill you. Which is worse, again?