Tetrahydrocannabinol, or THC, is the chemical or drug made in the cannabis that causes a person to feel different. It is similar to at least 113 other chemicals in cannabis, known as cannabinoids, but not all of them will make you feel different or high after using it. There are about 540 chemicals in cannabis total. THC is a very fatty chemical and doesn't interact with water very well. THC is thought to be used by the plant for protection from bugs, light, and other harm from its environment. The THC chemical structure was discovered in 1964 by Dr. Raphael Mechoulam and Dr. Y. Gaoni at the Weizmann Institute in Israel.