Marijuana is one of the most popular and most frequently taken psychoactive substances in the world. Therefore, it seems particularly important to know the influence of this plant on the human thought and behaviour. This paper reviews the impact of cannabis use on cognitive functioning. In cannabis, there are over 100 different active compounds known as cannabinoids. The ones known best include Δ9-tetrahydrocannabinol (THC) and cannabidiol (CDB). These two compounds workdifferently, i.e. THC impairs the learning process, increases anxiety and causes effects similar to psychosis, while CBD supports the learning process, working in antipsychotic and anxiolytic way. Furthermore, CBD may diminish the negative effects of THC, hence the influence of marijuana is largely dependent on the mutual proportions of these two compounds. It is believed that the cognitive deficits caused by the use of THC are operably linked to the areas of highest density of CB1 receptors in the brain. The research results are relatively compliant with regard to the negative effect of THC on learning and memory. Majority of research suggests
a slight deficit in executive functions associated with the use of marijuana in regular smokers. The results of longitudinal studies suggest no effect of marijuana on intelligence, when other relevant factors, such as use of nicotine and alcohol, are taken into account.