Or 'THC' for short. This is the chemical in marijuana that gets you HIGH.
When smoking medical marijuana, the amount of the cannabanoid delta-9 tetrahydrocannabinol (THC) in it will determine the psychoactive effect or head "high" the patient experiences. Cannabidiol or 'CBD' is the other cannabanoid found in marijuana and interacts with THC. CBD is known for providing positive effects to the body without the psychoactive (heady) effects.
by CaliforniaDispensaryInfo.com January 27, 2014