Why can cannabis be found in a drug test for longer than other drugs?

You've said in a previous post that cannabis can be found in a drug test much longer than other drugs. Why is that?

The time that cannabis (or any other drug) can be detected in the body can vary and is influenced by many factors. It can be different for each person, with the same individual possibly even getting different results each time they are tested. There are no guarantees in this area but it is certainly true that cannabis is likely to be identified in a drug test for much longer than other substances.

One of the main active components in cannabis is THC – that's what gets you stoned. Drug tests measure THC, or to be more specific a THC metabolite that shows your body has broken down THC. These metabolites can stick around in the body for a reasonable amount of time mainly due to the fact that when you use cannabis, unlike other drugs, it is stored in the body’s fatty tissue. It is then, over a period of time, released slowly back into the bloodstream.

Drugs such as amphetamine or cocaine are not stored in fat, leading to them leaving the body relatively quickly through a range of bodily functions such as urinating and sweating.

The length of time cannabis can be detected depends on what method of testing is used and the nature and extent of someone’s cannabis use. The more frequently and heavily cannabis is used the longer it may be detected in the body, especially in urine.  Drug tests in the workplace usually use saliva or urine tests. In Australia, police conduct roadside saliva tests for a range of drugs, including cannabis. Blood tests are expensive and invasive, so are used less frequently.

For an occasional light user, cannabis may be detected in the urine for 1 to 5 days following use. For frequent heavy users such as those people who use most days, cannabis may be detected up to 2 months or even longer. Most other drugs, even when used frequently or heavily, are only detectable in the urine for 1 to 3 days.

Cannabis can usually be detected in saliva for up to 6 hours, depending on the test procedure and the person. Government road safety guidelines in Australia state that cannabis can be detected for up to 12 hours in a saliva test. Some people have claimed that cannabis has been detected in their saliva beyond the 12-hour period, in some cases days and weeks after having used the drug.

Cannabis can usually be detected in blood for 24 to 36 hours after use.

First published: April 2018