AbstractBackground: Cannabis is the world’s most commonly used illicit drug, being used of about 4% of the total global population between 15 and 64 years of age. After the discovery of theendocannabinoid system there has been an increase in the research about cannabis and THCand its potential use as a therapeutical drug. Hence there has also been renewed interest in itspossible negative effects.Aims: To highlight recent knowledge and literature about the possible non-acute irreversibleeffects of long-term cannabis use on cognitive functions. And if possible draw conclusions onthe subject.Method: A systematical search on the databases Pubmed and Cochrane Library with keywords; cannabis, cannabinoids, hasjis, marijuana, cognition, cognitive dysfunction, learning,memory, long-term and non-acute. Among other inclusion criteria was a controlled abstinenceperiod from cannabis of at least 25 days for participants.Conclusions: 8 studies that matched all criteria. In two of these the authors concluded therewere no evidence for cognitive impairments 28 days or more after end of use. One of themwas the only longitudinal study with pre-THC-debut data of participants. A third study foundthat early-onset users exhibited poorer cognitive performance than late-onset users. Thisfounding was supported by yet another. The only meta-study found only small significantdifferences on the learning and forgetting domaines. Three studies also measured brainactivity in cannabis users and all found alterations compared to non-using controls, but onlyone also found dose-related differences in test performance.