Improving Interpretation of Drug Exposure: Implications for Evidence-Based Drug Policy

Abstract

A positive drug test may result in suspension of one's driving license, loss of employment, or removal of children from the home, making it imperative that multiple factors be considered when interpreting results. Controlled research is critical for providing the data to improve result interpretation. Two drug administration studies were conducted to address drug test interpretation of opiates, amphetamines and cannabis results. In the first, participants consumed two raw, uncooked poppy seed doses (15.7 mg morphine, 3.1 mg codeine per dose), and administered seven doses of intranasal l-methamphetamine (Vicks® VapoInhaler™) per manufacturer's recommendations. Positive OF morphine tests >2.5 h or positive OF codeine tests with a 15 µg/L confirmation cutoff suggest an alternate route of opiate exposure other than from poppy seeds. Prevalence of positive OF l-methamphetamine tests was ≤7.5% and last detection times were >32 h after the first dose with a 25 µg/L screening cutoff. Screening OF with a selective d-methamphetamine assay prevented positive test results. In the second, frequent and occasional cannabis smokers were administered placebo, smoked, vaporized, and oral (6.9% Δ9-tetrahydrocannabinol [THC], ~50.6 mg) cannabis. Cannabinol (CBN) and cannabigerol (CBG) were the best blood markers for identifying recent cannabis intake, but not after oral dosing. OF Δ9-tetrahydrocannabivarin (THCV) identified use within 10 h after all administrations, useful for driving under the influence of drugs (DUID), while OF CBG may identify use within 26 h, useful for daily drug treatment compliance programs monitoring relapse. Blood 11-nor-9-carboxy-THCV (THCVCOOH) or OF THCV or CBG also discriminated medicinal synthetic THC from intake of cannabis plant products. OF THC on-site screening devices demonstrated best performance with a 5 µg/L cutoff, but there were more true positive results with a 2 µg/L cutoff; an OF THC ≥2 µg/L confirmation cutoff is suitable for drug treatment programs to detect intake within 26-32 h. Oral cannabis intake significantly increased performance impairment in occasional smokers only. Partial tolerance to cannabis' subjective effects were observed in frequent smokers after all doses. Additionally, vaporization exposed users to significantly less carbon monoxide than smoking. These data improve result interpretation and guide development of evidence-based drug policies and legislation.