Marijuana is not a drug. Yes, it harms your lungs, no say against that. But you don't need to smoke marijuana to get high off of it. And just to let you know, your body creates the chemical that get's you high, THC. How does it create the chemical, you need to get hungry somehow, thats how you get hungry. Your body creates a smaller dose of THC to make you hungry, when your stomach is empty most of the time. THC is also a pain reliever, which when you are in pain, a low dose of THC is created in your blood stream to help cope with the pain. Sure it don't work, but it's all worth the try.
Ok, well I will go with it's a drug then. But it can be both, depending on how you put it. All plants have chemicals in them. So here...
a chemical substance used in the treatment, cure, prevention, or diagnosis of disease or used to otherwise enhance physical or mental well-being. - Drug
Herb - such a plant when valued for its medicinal properties, flavor, scent, or the like.
Ok, I prove my point, well kinda. It's a drug, but it's an herb...