Objective: This review summarises the existing evidence on the effects that recreational and medical use of cannabis and cannabinoids have on cognitive performance. Methods: Databases (PubMed, Medline, and Google Scholar) were searched from inception to March 2017 by adopting the following key terms: dronabinol, nabilone, nabiximols, cannabis, marijuana, cognition, neurology, and neuropsychology. A total of 94 documents, including reviews, preclinical and clinical studies, industrial and government agencies reports were included in this review. Results: We found that recreational use of cannabis doubles the risk of a fatal traffic accident by impairing attention and lengthening reaction time. Short-term use lowers performance in working memory, attention, executive functions and visual perception tasks. Chronic recreational use in adolescents also doubles the risk of early school-leaving, cognitive impairment and psychoses in adulthood. Adverse effects of cannabis-based medication – dronabinol, nabiximol and nabilone – and ingestion/inhalation of marijuana allowed for medical use include dizziness, drowsiness and short-term memory impairment. Conclusion: Cannabis consumption is associated with significant impairments in a range of cognitive abilities. Of particular concern, early and chronic exposure to cannabis, especially in the adolescence, seems to be associated with irreversible cognitive impairments.