Difference between hemp and marijuana It’s a common misconception that hemp and marijuana are two different species of plant. In fact, they’re not distinct species Trusted Source at all. They’re just two different names for cannabis, a type of flowering plant in the Cannabaceae family. While science doesn’t differentiate between “hemp” and “marijuana,” the law does. Legally, the key difference between the two is tetrahydrocannabinol (THC) content. THC is one of many cannabinoids, or chemicals found in the cannabis plant. It’s the one that’s primarily responsible for the “high” associated with cannabis. What is hemp? The term “hemp” is used to mean cannabis that contains 0.3 percent or less THC content by dry weight. Why 0.3 percent? This definition was first proposed in 1979, in a book called “ The Species Problem in Cannabis: Science & Semantics .” In the book, author Ernest Small addresses the fact that it’s difficult to distinguish hemp and cannabis because there’s no a