Identifying EEG markers related to acute cannabis consumption: A systematic review.

Background/rationale: Electroencephalography (EEG) has potential to provide a sensitive measure of the acute neurophysiological response to cannabis administration. As delta-9-tetrahydrocannabinol (THC; the psychoactive constituent of cannabis) can induce transient neurocognitive impairments that differ as a function of tolerance and dose, understanding the neural profile related to intoxication would be of great benefit in the wake of increasing recreational and medicinal use. Accordingly, the present systematic review examined the current research literature related to acute cannabis administration and EEG measures.

Methods: Peer-reviewed articles published from 2000 were assessed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Studies that administered non-synthetic cannabis, containing THC (orally or inhaled) and reported differences in EEG outcomes within the acute time frame (<6hours post-administration) as compared to baseline or placebo, were eligible for inclusion.

Results/discussion: A total of 16 studies were eligible for inclusion, of which 11 reported differences in the amplitude/latency of event-related potentials (ERPs) and 9 reported changes in frequency band power. Of the ERPs, the P3 was identified as a potential indicator of recent cannabis consumption, as demonstrated by decreased P3 amplitude across various doses (generally exhibiting small-to-moderate magnitude effects where effect sizes were reported). Oscillatory activity in the theta frequency band power range (typically 4-7Hz) was impacted following cannabis administration, with some support for a dose-dependent change in power. The present results highlight the potential utility of some EEG measures as markers of recent cannabis consumption, although great heterogeneity in participant characteristics and reported data limits conclusions from these results. It is also evident that EEG changes in highly tolerant user groups (such as those who use cannabis medicinally), require further exploration.