Employers or people who work in a government agency, like the police or FBI, may test someone to see if they used any drugs recently. This is called a . Police may do this if they think you have used marijuana before or while you are driving a car. THC lasts a long time in the body and can be found in body fluids, like urine or saliva, or hair and sweat. Since it lasts so long in the body, it can be a problem being sure if someone is high. 