Cannabis is one of the most widely used substances worldwide with an estimated global prevalence of 2.7 – 4.9 (UNODC, 2017) percent and a lifetime-use of 78 percent (Global Drug Survey, 2017). Its sought-after psychoactive effects include relaxation, euphoria and dreaminess, but it can also lead to feelings of anxiety and paranoia. Cannabis contains more than 600 compounds, including over 85 different cannabinoids, which have been recognized for both their toxic and potential therapeutic effects, and which exert their effects through the endogenous cannabinoid system. Delta-9-tetrahydrocannabinol (commonly known as Δ9-THC or THC) is considered to be the primary psychoactive constituent present in cannabis responsible for the acute effects of cannabis on various cognitive functions including memory and attention. In contrast, the other major cannabinoid that has attracted attention in recent years, cannabidiol (CBD), is non-psychoactive and might have anxiolytic and antipsychotic effects.
Laboratory studies by our group have investigated neurocognitive performance and neurophysiological functioning during THC-intoxication as well as cannabinoid pharmacokinetic properties in both occasional and heavy/chronic users. Our work on cannabis-induced cognitive impairments has specifically focused on performance tests measuring skills related to driving, such as perceptual motor control, motor impulsivity, and cognitive function. Moreover, the impairing effects of high-potency cannabis on executive function and inhibitory motor control have been studied, and we have tested whether the cannabis-induced memory impairment is mediated via glutamatergic or cholinergic pathways.
Ongoing studies include investigations of cannabis-induced neuroadaptations (using fMRI), field and laboratory experiments examining memory for a criminal event during and after cannabis intoxication, and an investigation of THC and CBD-induced driving impairment. In addition, we are also conducting a study into the effects of synthetic cannabinoids (see NPS).
A comparison of performance on several neurocognitive tasks between occasional and heavy users is pictured below.
Distribution of observations showing ‘impairment’ or ‘no impairment’ for THC concentrations lower or higher than 10 ng/ml in the critical tracking task (CTT), divided attention task (DAT) and the stop signal task (SST). Taken from Ramaekers et al., 2008.