There are lots of different ways to test for traces of cannabis in a person’s system. Urine testing is by far the most common method of drug testing, especially by an employer. These samples are often collected on-site and then sent to a laboratory to be tested. THC can also be detected in hair, saliva, and blood. Since urine is the most common method of testing, how long after you smoke cannabis will THC be found in your urine? Read more here.