Herzig, D. 1, 2, 3 , Nutt, D. 4 & Mohr, C. 1, 2
1 Institut de Psychologie, Université de Lausanne, Lausanne, CH
2 Department of Experimental Psychology, University of Bristol, Bristol, UK
3 Institut universitaire de médecine sociale et préventive Lausanne, Lausanne, CH
4 Psychopharmacology Unit, Imperial College London, London, UK
Cannabis use negatively affects certain frontal lobe functions, particularly in psychotic and psychosis-prone individuals. Schizotypy -a milder form of schizophrenia symptoms in the general population- also negatively influences these functions. Interestingly, cannabis use is elevated in schizotypy, making schizotypy a likely risk candidate to predict use and harmfulness of cannabis use. We therefore followed up 12 pure cannabis users and 30 non-cannabis users (controls), and assessed their schizotypal symptoms and frontal lobe functions (response inhibition, cognitive flexibility, verbal short-term memory and working memory) at baseline, 6 months and 12 months later. Results showed that cannabis users had a significantly worse verbal short-term memory performance than controls at baseline. Response inhibition performance improved over time in both groups. Neither frequency of cannabis use nor schizotypy related to task performance. These results suggest that cannabis use a) is associated with attenuations in verbal short-term memory, b) does not lead to a worsening of frontal lobe functioning within a year, and c) and schizotypy do not predict attenuations in frontal lobe functions measured here. Future studies should consider testing non-student populations, and further elucidate whether previous reports on detrimental effects of cannabis might be explained by polydrug rather than cannabis use.