OK, pop quiz time.
Which of these activities is the most harmful to your health?
1. Smoking Tobacco.
2. Smoking Basil.
3. Smoking Coffee. (I don't know if this would deliver caffeine effectively...)
4. Smoking Marijuana.
5. Smoking any other non-poisonous plant.
If you answered 1, you're wrong. According to the articles I've seen on New Scientist, #4 is slightly worse for you (mainly, my guess is, because Marijuana is not grown in controlled conditions and is more likely to have other dangerous things in it). But these activities all do approximately the same amount of harm to your body.
Here's the scoop. SMOKING ANYTHING IS BAD FOR YOU. And, guess what? IT'S THE SMOKE ITSELF THAT DOES THE HARM. Nicotine is not the main culprit behind lung cancer, though it certainly does your body no good. It's the burned plant matter that does the damage!
Breathing in burning things is bad for you, big surprise. So, if you smoke and don't want to quit, consider switching to another form of nicotine delivery. Still bad for you, but nowhere near AS bad for you. (for more reading...)
And switch to brownies if you're doing the other stuff...