Yea, THC is a psychoactive substance (it causes psychosis: A severe mental disorder in which thought and emotions are so impaired that contact is lost with external reality). It's actually quite interesting.. the only reason you don't trip balls like acid and have your personality changed on you, is that cannabis also contains a substance called cannabidiol. Cannabidiol counteracts the effects of THC. http://en.wikipedia.org/wiki/Cannabidiol Cannabidiol is the element of cannabis that has currative properties and inhibits cancer cell growth.