THC, or tetrahydrocannabinol, is the chemical responsible for most of marijuana’s psychological effects. It acts much like the cannabinoid chemicals made naturally by the body. THC is one of many compounds found in the resin secreted by glands of the marijuana plant. More of these glands are found around the reproductive organs of the plant than on any other area of the plant. Other compounds unique to marijuana, called cannabinoids, are present in this resin.