Cannabis (aka weed, marijuana, or ganga) is the product of the cannabis plant, prepared for use as a psychoactive drug and as a medicine. Its use stretches as far back as history itself and is one of the earliest known plants to be domesticated by man. Cannabis, or weed, is the fourth most widely used drug in the world after coffee, alcohol, and tobacco. But unlike coffee, alcohol, and tobacco, weed is illegal in most of the world and is, therefore, the world’s most widely used illicit drug. The complexity of this plant and its relationship with man becomes obvious when it is categorized pharmacologically. Whereas most psychoactive drugs fall clearly into a single category of stimulant, depressant, or hallucinogen, cannabis cannot be so easily constrained, possessing as it does all of these capabilities and more. The difficulty in classifying cannabis is also evidenced in its effects, which can feature elements or symptoms of all other drugs. Sometimes weed can change the user’s mood (for better or worse), and at other times it can magnify the user’s existing mood. Open this book and enter the world of weed.