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Illicit drug use correlates with negative urine drug test results for prescribed hydrocodone, oxycodone, and morphine.

BACKGROUND
A number of studies indicate that 10.8%-34% of patients with chronic pain use illicit drugs. One hypothesis for this occurrence is that some patients may be supplementing their prescription medications with illicit drugs.


OBJECTIVE
The primary purpose of this retrospective data analysis was to test the hypothesis that people whose urine specimens are positive for the medications that have been listed as being prescribed to them are positive for fewer illicit substances than those whose specimens were negative for their prescribed medications. The secondary purpose of the study was to correlate the use of illicit drugs and the amount of prescribed medications excreted in urine.


STUDY DESIGN
A retrospective study of the incidence of patients using illicit drugs versus their consistency with reported medications.


METHODS
Using urine specimens from a cohort of nearly 400,000 patients whose identities had been redacted, and who were being treated for chronic pain with opioid therapy, this study was performed to correlate the patients' positivity with their prescribed medication to the prevalence of illicit substance use. A secondary study was conducted to correlate the amount of prescribed medication excreted in urine (measured in ng/mL) with the incidence of illicit drug use. The specific prescription medications analyzed were hydrocodone, morphine, and oxycodone.


RESULTS
Specimens defined as negative for prescribed hydrocodone (27.3%), morphine (11.5%) or oxycodone (19%) were more likely to contain illicit drugs than those found to be positive for the prescribed medication. The illicit drug prevalence among the inconsistent specimens was 15.3% for hydrocodone, 23.8% for morphine, and 24.4% for oxycodone. The secondary study showed no statistically significant difference in the excretion level of prescribed medication between those patients using and not using illicit drugs.


LIMITATIONS
The study is limited in that no data was obtained to determine the causal relationships of illicit drug use.


CONCLUSIONS
This work supports the hypothesis that people who are positive for their prescribed medications use fewer illicit drugs than those who do not take their medications. It may be beneficial for physicians to test more thoroughly for illicit drugs when patients' drug tests are negative for their prescribed medications.