Marijuana is a preparation of the Cannabis plant intended for use as a psychoactive drug and as medicine. The principal psychoactive constituent of cannabis is tetrahydrocannabinol.
Cannabis is often consumed for it's psychoactive and physiological effects which can include heightened mood or euphoria, relaxation, and increase in appetite.
Dr. James C. Munch testified in court, under oath, stated that he had smoked marijuana, and that marijuana would make your fangs grow six inches long and drip with blood, and when he tried it, it turned him into a bat!
Dr. Munch was the official expert on marijuana for the U.S. Government from 1938 to 1962. We don't know if his name is where the term 'munchies' came from, or if it's just a delicious irony.