The amount of time that your body retains traces of marijuana depends on a number of factors, including how often you smoke and your metabolism rate.
Urine testing, or urinalysis, is the most common way of screening for marijuana use. In the United States, current and future employers will often ask you to undergo a urine test.
But how long will marijuana show up in your urine after you stop smoking? Unfortunately, the only accurate answer is: It depends.
THC vs. THC-COOH
THC is the active ingredient in marijuana and the chemical responsible for the high. However, urine tests detect a different chemical called THC-COOH.
THC-COOH is a metabolite of THC. It is produced when the liver breaks down THC and stays in the body for much longer.
The most common cutoff level for THC-COOH used by drug screening companies is 50 ng/mL. Less common cutoff levels are 20 ng/mL and 100 ng/mL.
Length of Detection Period
No one can really say how long you will test positive for marijuana, since the rate of THC metabolism varies per individual. The amount of marijuana consumed can also alter the window of time that your body retains traces of THC.
Even still, studies provide some insight into how long the average individual will test positive for marijuana.
Someone who smokes occasionally – or for the first time – will likely test positive for 1-3 days afterward, according to a review by the National Drug Court Institute (NDCI).
But by the end of 4 days, infrequent cannabis users should be safely below the 50 ng/mL threshold.
“For occasional marijuana use (or single event usage), at the 50 ng/mL cutoff level, it would be unusual for the detection of cannabinoids in urine to extend beyond 3-4 days following the smoking episode.”
Studies suggest someone who smokes often can expect to test positive for around a week following last use. According to the NDCI, after 10 days, most frequent users should pass a urine test at the 50 ng/mL threshold.
“Based upon recent scientific evidence, at the 50 ng/mL cutoff concentration for the detection of cannabinoids in urine, it would be unlikely for a chronic user to produce a positive urine drug test result for longer than 10 days after the last smoking episode.”
However, there’s no guarantee that a heavy cannabis smoker will be free of THC metabolites after 10 days. Studies show it’s possible for some users to test positive for up to a month after last use.
In one extreme case, a person who reported using cannabis heavily for over 10 years managed to test positive (above 20 ng/mL limit) for up to 67 days after last use.
How To Pass A Urine Test
While there are a number of products being marketed as urine cleansers, there is probably good reason to be skeptical of their claims.
Drinking an excessive amount of liquid may be the most scientific solution, since it would naturally dilute anything found in your urine.
But drinking too much water could spoil the sample. Urine that is too diluted may be identified and rejected by the testing lab as possibly being tampered with. Still, this could buy some time for a retest, depending on the circumstances.