Myth: Confirmed levels of metabolite concentrations in urine are directly proportionate to usage (i.e. the more drug you take, the more you have in your system)
Fact: There are several studies discussing how drug metabolite disposition varies among individuals and dosage levels. In the previously referenced manuscript by Dr. Marilyn Huestis and Dr. Edward Cone, the purpose of the study was to “review the disposition of methamphetamine in oral fluid, plasma, and urine.” In the study, they administered single and multiple doses of methamphetamine to 5 non-drug users. The multiple-dose study included Subject BB receiving sequential doses of 20 mg methamphetamine (given at 0, 24, 48 and 72 hours), as well as Subject S receiving non-sequential doses of 10 mg methamphetamine (given at roughly 0, 48, 72 and 144 hours). Although Subject BB ingested twice as much drug during the study, Subject S demonstrated considerably higher levels of methamphetamine in the urine. While this study focuses on the different detection times in oral fluid, plasma, and urine, it also shows that the disposition of drugs in a bodily fluid is NOT necessarily directly proportionate to dosage or ingestion. Besides individual variations, concentrations of drugs in these liquid matrices are completely dependent on the time lapsed between ingestion and sampling, and therefore results can never be used to indicate the magnitude of the dose.
In Summary
When constructing a program that ensures a drug-free workplace, it is always important to understand facts versus myths. Highlighted in this six-part blog series are just some of the common myths in the industry. It is always a good idea to reach out to your drug testing professionals to get the most up-to-date information and to ensure that your program is not being influenced by any of these or other common misconceptions.