Objective: In our study, it is aimed to investigate impacts of cannabis use on information processing and psychomotor functions and to examine changes in the cognitive functions at the end of abstinence over a month. Method: The study was initiated with 34 volunteer participants using cannabis at least over two years, directed by a forensic unit. 34 persons were assessed at admission and were planned to assess after a month of remission. As 14 participants discontinued the study 20 participants only were assessed again at the end of a month. The participants were applied The Montreal Cognitive Assessment (MOCA) test, Edinburgh Handedness Inventory, Finger Tapping Test (FTT), Adult Memory and Information Processing Battery (AMIPB) A and B, and simple reaction time tests (auditory and visual) in admission and were applied Finger Tapping Test (FTT), Adult Memory and Information Processing Battery (AMIPB), and simple reaction time tests (auditory and visual) at the end of a month. Results: There was no statistically significant difference between participants continue to the treatment and those discontinue in terms of sociodemographic and clinical characteristics. The participants discontinue were using more daily cannabis dose. The auditory reaction time of the group continue to the treatment decreased statistically significantly after a month whereas there was no statistically significant difference in the visual reaction time. The scores of the AMIPB-A and AMIPB-B were detected statistically higher after a month compared to admission. The score of the dominant hand FTT after a month was detected statistically higher than that in admission whereas there was no statistically significant difference in the non-dominant hand score. Conclusion: Improvements in scores of AMIP-A, AMIP-B, FTT and auditory reaction time after one month of quitting cannabis suggest that cannabis use may impair cognitive functions such as information processing, reaction time and motor functions. We suggest that future studies to assess cognitive functions after either a shorter (i.e. 1 week) or a longer (i.e. 2 months) period of cannabis abstinence in larger samples may provide further useful data about the relationship between cannabis use and cognitive functions.