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From: Robert Swotinsky MD
Password: orange
Date: 17 Oct 2006
Time: 15:16:50 -0700
Remote Name: 71.192.169.156
A ratio of 0.5 or greater between two creatinine-normalized positive cannabinoid tests can help differentiate new marijuana use from residual excretion. [Huestis MA, Cone EJ. Differentiating new marijuana use from residual drug excretion in occasional marijuana users. JAT 1998;22:445-54]
The situation posted describes marijuana-positive drug tests that are being attributed to use more than two months ago. Some research has demonstrated that chronic marijuana users can have positive test results for cannabinoids for 3 or more weeks after last use, but not more than 2 months after last use. You can conclude that anyone testing positive for marijuana in mid-October is not testing positive because of last use in August.