There are 4 main types of drug tests that can detect the presence of THC in your system: Urine, Blood, Saliva and Hair tests.
Urine Drug Tests:
Urine tests are the most common means of drug detection available in the United States, especially in workplace drug testing programs. They are also the least expensive and can be performed in-home without supervision. Compared to blood tests, urine tests are non-invasive, although they are more invasive than both saliva and hair tests. One important thing to note about urine tests specifically for THC is the inability to detect current impairment. A urine test that shows a positive result for the presence of THC does not prove the subject is impaired at the time of testing. It simply means they used marijuana in the recent past. Urine tests for THC can also not specify frequency of use or dosage amounts either. This is especially important in the testing for marijuana DUI cases.
Blood Drug Tests:
Blood testing is the least commonly used drug testing method because of its high level of invasiveness, as well as the requirement of medically trained personnel. They are also the most expensive drug tests on the market. However, blood tests are the most accurate and have the most recent window of detection, usually with a few hours of use.
Saliva Drug Tests:
Saliva tests are relatively common because they are inexpensive and easy to use. They can be performed at home without supervision and are generally seen as non-invasive. Saliva tests can usually detect the presence of THC anywhere form a few hours after use up to one week.
Hair Drug Tests:
Hair tests are by far the least invasive testing method on the market, but they are also significantly more expensive than urine and saliva tests. Hair tests usually require a 1.5 inch sample of hair and can detect use for the past 90 days. However, due to the growth rate if hair, the test cannot account for the past week of use.