Because they are both cannabinoids, THC and CBD have an exact similar chemical structure. Each molecule of CBD and THC has 2 oxygen atoms, 30 hydrogen atoms, and 21 carbon atoms. However, it’s Robert S Cahn, a British chemist, who is often credited for discovering the first cannabinoid – cannabidiol, which was isolated a couple of years later by US chemist Roger Adams. William B. O’Shaughnessy started investigating the therapeutic properties of CBD-rich cannabis. The difference in name is mostly a function of a legal definition, which sets the threshold for THC content. The flowers of a hemp plant contain little to no THC, while the flowers of a cannabis plant contain much higher levels of THC. Industrial hemp contains less than 0.3% THC, and as such, it is considered legal under federal law to cultivate, harvest, and process into finished products. Cannabis, on the other hand, contains more than 0.3% THC and remains federally illegal.