False Positives in Drug Testing

Certain preliminary “screening” tests commonly used by police in field testing (example: immunoassay) for possible drug use are NOT SPECIFIC for marijuana, cannabis or the metabolites (burn-off substances produced as your body eliminates the drug).  The standard police “THC test” is a one-step rapid, qualitative immunoassay for the detection of tetrahydrocannabinol compounds in urine. The cutoff concentration for a positive result in an immunoassay test is 50 ng/ml as recommended by the Substance Abuse and Mental Health Services Administration SAMHSA) (NIDA). To truly determine whether the suspected “drug” was from marijuana or cannabis, a SECOND, more sophisticated test must be conducted.  This is called a gas chromatograph/mass spectrophotometer test (GC-MS). This device permits IDENTIFICATION and QUANTIFICATION of specific amounts of cannabinoids that are ONLY produced when cannabis or marijuana has been used. The cutoff for GC-MS is 15 ng/ml, according to the Substance Abuse and Mental Health Services Administration (SAMHSA) (NIDA).

Substances or Health Conditions that can cause false “marijuana” positives:

OVER-THE-COUNTER DRUGS

PRESCRIBED DRUGS

Promethazine (Phenergan, Promethegan)
Dronabinol (Marinol®)

HEALTH CONDITIONS

Liver Disease
Kidney infection (Kidney disease, diabetes)