Cannabis and marijuana both belong to the same species, marijuana, and the two plants look somewhat similar. However, a large amount of variation can exist within a species. After all, a Great Dane and a Chihuahua are both dogs, but they have distinct differences.
The decisive difference between hemp and marijuana is their psychoactive component: tetrahydrocannabinol, or THC. Hemp has a THC content of 0.3% or less, which means that cannabis-derived products don’t contain enough THC to produce the “high” traditionally associated with cannabis.
CBD is a compound found in cannabis. There are hundreds of such compounds, known as "cannabinoids" because they interact with receptors involved in functions as diverse as appetite, anxiety, depression and pain perception. THC is also a cannabinoid.
Clinical studies have shown that CBD is effective in treating epilepsy. Anecdotal evidence suggests it can help with pain and even anxiety -- though the science is inconclusive.
Marijuana, which contains CBD and more THC than hemp, has been shown to be therapeutic for people with epilepsy, nausea, glaucoma and even potentially multiple sclerosis and opioid dependence.
However, medical research on marijuana is strictly limited by federal law.
The Drug Enforcement Administration classifies marijuana as a Schedule 1 substance, meaning it treats it as if it has no recognized medical use and a high potential for abuse. Scientists don't know exactly how CBD works, nor how it interacts with other cannabinoids like THC to give cannabis its extra therapeutic benefits.