Abstract
Human performance studies have usually relied on low-potency marijuana (4% THC) for determining THC-induced impairment. The present study was designed to assess the effects of high-potency marijuana (13% THC) on human performance. In all, 20 recreational users of marijuana participated in a double-blind, placebo controlled, three way cross-over study. The treatments consisted of single doses of 0, 250, and 500 μg/kg THC. Performance tests were conducted at regular intervals between 15 min and 6 h postsmoking and included measures of motor control (Critical tracking task), executive function (Tower of London) motor impulsivity (Stop signal task), and risk taking (Iowa gambling task). THC significantly impaired performance in the Critical tracking task and decreased the number of correct decisions in the Tower of London task. In addition, THC significantly increased stop reaction time and the proportions of commission and omission errors in the Stop signal task. THC-induced impairments lasted up to 6 h postsmoking as indicated by the absence of a THC × Time after smoking interaction. Effect sizes for performance impairments produced by THC 250 μg/kg were relatively low but generally increased by a factor of two in case of THC 500 μg/kg. These data suggest that high potency marijuana consistently impairs executive function and motor control. Use of higher doses of THC in controlled studies may offer a reliable indication of THC induced impairment as compared to lower doses of THC that have traditionally been used in performance studies.
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Acknowledgements
This study was supported by grants from the German Federal Police Academy and the German Society against Alcohol Drugs and Driving (‘Bund gegen Alkohol und Drogen im Straßenverkehr’). We thank Anita van Oers, Janneke Guyaux and Roland Otten for their contributions to study logistics and data collection. We are grateful to Elke Runow, Volker Schwarz, Werner Pogoda and Markus Düchardt for their technical assistance. We thank Chip Walls for his literature ‘search engine’.
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Ramaekers, J., Kauert, G., van Ruitenbeek, P. et al. High-Potency Marijuana Impairs Executive Function and Inhibitory Motor Control. Neuropsychopharmacol 31, 2296–2303 (2006). https://doi.org/10.1038/sj.npp.1301068
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DOI: https://doi.org/10.1038/sj.npp.1301068
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