Cognitive Deficits in Marijuana Users


  • About 14.6 million people in the US use marijuana, 36% of which have the related disorders that require appropriate interventions.
  • Various approaches, such as cognitive-behavioral therapy, have been adapted for marijuana patients. However, the assumption that patients possess adequate cognitive functioning makes it difficult for patients with less cognitive abilities to complete therapy.
  • Neuropsychological testing for marijuana patients is required since most clinical variables that affect cognitive functioning remain largely unknown.
  • Subjective reports show that marijuana users have low concentration, attention, impaired memory, and decision execution problems.
  • These factors established the need to study cognitive functioning in marijuana patients to provide adequate data on these individuals’ treatment outcomes based on cognitive behavioral and motivational enhancement therapy.
  • The research aimed at studying the level of cognitive functioning and clinical variables that affected the treatment outcomes of marijuana dependent patients.


Study Method

20 participants were recruited in a quantitative experimental study. The marijuana dependent patients were subjected to randomized controlled trials for 12 weeks. Therapies included motivational enhancement therapy (MET) and cognitive behavioral therapy (CBT), combined with nefazodone and buproprion medication.

Inclusion Criteria

The respondents were aged between 18 and 50 years and met the DSM-IV characteristics of patients with marijuana dependence.

Exclusion Criteria

  • If patients met the current criteria of DSM-IV disorders that required intervention
  • If participants were addicted to other substances instead of cannabis
  • The patient had a current prescription of psychoactive drugs

If the participant had a history of a learning disability

Patient Population

The enrolled participants were 20 marijuana dependent patients


  • The level of cognitive functioning in patients addicted to marijuana
  • The clinical outcomes of CBT+ MET therapy and medication on marijuana dependent patients

Statistical Analysis

  • Statistical tests included Levene’s test that tests normality assumptions and homogeneity of variance.
  • MicroCog subsets showed a significant skew with z-scores between 0.002 to -2.631
  • Completed Categories and Failure scores and those of WCST z-scores were -3.50 and 2.92
  • Wilcoxon Exact Test measured the cognitive functioning in both completers and dropouts
  • The General Cognitive Proficiency was used to measure high and low cognitive functioning

Fisher’s Exact Test measured the differences in patients’ proportions based on cognitive functioning levels and whether they were complete or dropouts.


  • The study revealed that 7 completers and 13 dropouts, and this number was not significantly different on the mean age, education, and mean years.
  • The standard deviation for completers was 5.0 for completers mean average of 30.0 years and 9.6 for dropouts with a mean age of 31.2 years.
  • Based on full-time employment, 57% were completers while 46% dropouts.
  • 29% of completers used alcohol, while only 15% of dropouts were alcoholics: for cocaine, the percentage was 0% and 15%, respectively.
  • The participant used marijuana in the previous 30 days before the study, and the urine tests only revealed marijuana as the only substance.
  • Fisher exact test revealed a p=0.10 ( no significant difference in retention between completers and dropouts)
  • Based on marijuana abstinence, Kruskal-Wallis test and chi-square revealed=0.64b, p=0.7 and df=2
  • Tetrahydrocannabinol (THC) levels mean were 617.5 ng/mL with a standard deviation of 603.3.
  • THC’s mean levels did not differ after battery with 635.1 and SD 943.1 for completers and 607.9 and SD 362.3.
  • Wilcoxon Test revealed a confidence interval of p=0.35.
  • Based on cognitive functioning and treatment retention, the MicroCog scores for completers were 0.5 standard deviations above the mean and nearly 1 standard deviation near the population mean.
  • Dropouts showed lower scores of abstract reasoning, accuracy, and spatial processing. This means that completers showed a 0.5 SD above; meanwhile, dropouts indicated a 0.5 SD below the population mean.

Primary Outcome

The completers showed a higher cognitive ability based on accuracy, spatial ability, and mental reasoning. Lower cognition levels corresponded to dropouts and their treatment entry.

Secondary Outcome

  • WCST scores used to measure the difference between cannabis smokers and controls after abstinence were not informative to predict the treatment outcome.
  • Dropouts performed lower on abstract reasoning, which did not support the hypothesis.

The GCP score did not correlate with marijuana abstinence



  • A quantitative approach was applied with statistical analysis that shows patterns and trends of the variables being measured.
  • Other strengths included an excellent participation rate and carefully determined exclusion and inclusion criteria.

The recruited patients were marijuana dependent, and the neuropsychological analysis was extrapolated from similar studies performed on cocaine-dependent patients.


  • The study did not investigate the impacts of acute and residual effects of cannabis. Furthermore, it did not test pre-morbid impairment or that which is secondary to dependence on marijuana.
  • The research depicted a high dropout rate, which might have impaired the results
  • There was no post-follow-up data and an N limited analysis

Assessment of urine tests was not sensitive to short-term cannabis abstinence.


Author’s Conclusion

  • The study provides insight into marijuana dependence for further research.
  • The authors conclude that marijuana causes a degree of cognitive impairment.
  • The clinicians can consider shorter therapies as memory aids to enhance behavioral interventions.

My Conclusion

Cognitive impairment is closely related to marijuana dependence since there is a difference between the entry-level treatment between completers and dropouts. The study showed a considerable link between cognitive function and treatment outcomes, which is an imperative finding as it can assist in developing a deeper understanding of marijuana dependence and cognitive abilities.

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PsychologyWriting. (2022, January 31). Cognitive Deficits in Marijuana Users. Retrieved from


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"Cognitive Deficits in Marijuana Users." PsychologyWriting, 31 Jan. 2022,


PsychologyWriting. (2022) 'Cognitive Deficits in Marijuana Users'. 31 January.


PsychologyWriting. 2022. "Cognitive Deficits in Marijuana Users." January 31, 2022.

1. PsychologyWriting. "Cognitive Deficits in Marijuana Users." January 31, 2022.


PsychologyWriting. "Cognitive Deficits in Marijuana Users." January 31, 2022.