Table 1.

Studies that Investigated Cannabis Use and Cognition Association in Schizophrenia

Studies	Sample	Cannabis Criteria	Cannabis Use	Other Drugs	Cognitive Tests	Results
Lifetime history
Joyal et al27	16 SCZ + SUD14 SCZ −SUD	Cannabis abuse or dependency Not all the patients use cannabis but cannabis was the preferred substance for the sample	No information regarding abstinence and duration/onset of cannabis use		TMT-A, TMT-B, WCST, COWAT, RCFT, WAIS PA, Porteus Maze, Go/No Go	Impaired WCST, COWAT in nonusers Fewer neurological soft signs
	Stirling et al33	24 SCZ + CANN39 SCZ − CANN	Cannabis use prior to onset of psychosis	No information regarding abstinence and duration/onset of cannabis use		Design memory, verbal fluency, WAIS OA, BD, PC, PA, face recognition memory	SCZ + CANN better in 7/9 measures SCZ − CANN more deficit schizophrenia and more neurological soft signs
Jockers-Scherubl et al19		19 SCZ + CANN20 SCZ − CANN39 HC	At least 0.5 g daily For 2 y prior to onset	Abstinence, at least 4 wk (weekly urine screenings)	Alcohol excluded, SCZ − no other substance abuse	CPT-IP, TMT-A, TMT-B, WCST, WMS-R verbal and visual memory, WAIS-R (BD, PA, DSST, Comprehension)	SCZ + CANN performs better than SCZ − CANN in some cognitive domains. Regular use before 17 associated with even better performance
	Sevy et al32	14 SCZ + CANN13 SCZ − CANN	Cannabis abuse or dependency 0.5 g/day, >4 d of the week. Only 1 subject used in last 2 mo	No information regarding abstinence and duration/onset of cannabis use 78% started prior to onset of psychosis	Cannabis main substance, 7 alcohol abuse, 3 cocaine abuse Nicotine use is more in SCZ + CANN	WRAT, CPT-IP, CVLT, DS (backward and forward), TMT-A, TMT-B, COWAT (semantic and phonemic), IGT	No difference No impact of alcohol
		Løberg et al29 (Study I)	13 SCZ + CANN18 SCZ − CANN	History of cannabis abuse or dependency	No information regarding abstinence and duration/onset of cannabis use	All abuse cannabis 8 additional substance abuse mainly amphetamine	Memory, attention, psychomotor speed, general abilities, and executive function domains based on various test	SCZ + CANN performs better except memory
Schnell et al20	35 SCZ + CANN34 SCZ −CANN		Cannabis abuse or dependency All started prior to onset of illness (average 6 y)	Minimum 3 wk abstinence (self and medical reports and urine screening) Age of onset = 17 Duration = 8.5 y Frequency/month = 53 joints	No other substances except nicotine	AVLT, LNS, DSST, TMT-B, MWT-B, CPT, Verbal fluency, Dual processing task	SCZ + CANN better in WM, executive functions, and verbal memory. High frequency use was associated with even better performance
	Current/recent use
Potvin et al28	44 SCZ + CANN32 SCZ − CANN	Abuse or dependence Not all the patients use cannabis but cannabis was the preferred substance for the sample Last 6 mo	No information regarding abstinence and duration/onset of cannabis use	12 cocaine, 17 polysubstance	PAL, MOT	SCZ + CANN better in MOT No difference for PAL. However, SCZ + CANN patients who use cocaine are more impaired in PAL. Non cocaine user but SCZ + CANN patients are better than SCZ − CANN in PAL
	Løberg et al29 (Study II)	13 SCZ + CANN13 SCZ − CANN	Current cannabis abuse or dependency Acute admission with schizophrenia or schizophrenia like psychoses	No information regarding abstinence and duration/onset of cannabis use	All abuse cannabis 10 also abuse other substances (4 amphetamine, 3 cocaine, 4 alcohol)	Global cognition score based on various cognitive tests longitudinal study, 3 mo follow-up	In acute admission, SCZ + CANN performs worse, in follow-up they significantly improved SCZ − CANN no change in follow-up
Ringen et al78		117 SCZ + CANN23 SCZ − CANN	Cannabis use in last 6 mo			DSST, Digit span, 2-Back, Verbal fluency, Logical memory, word interference, CVLT	SCZ + CANN performs worse in verbal memory and attention
	Scholes et al79	22 SCZ + CANN	Current cannabis use			Stroop, WCST, Spatial span, LNS	No difference
49 SCZ − CANN

Note: TMT-A, Trial Making Test—Part A; TMT-B, Trial Making Test—Part B; TMT B/A, Trial Making Test—Part B minus Part A; WCST, Wisconsin Card Sorting Task; COWAT, Controlled Oral Word Association Task; RCFT, Rey Complex Figure Test; PAL, Paired Associate Learning; MOT, Motor Screening; OA, Object Assembly; BD, Block Design; PC, Picture Completion; PA, Picture Arrangement; DS, Digit Span; WAIS, Wechsler Adult Intelligence Scale, WRAT, Wide Range Achievement Test; CPT-IP, Continuous Performance Task—Indentical Pairs; CVLT, California Verbal Learning Task; IGT, Iowa Gambling Task; RAVLT, Rey Auditory Verbal Learning Task; LNS, Letter Number Sequencing; DMST, Delayed Matching to Sample Test; MWT-B, Mehrfachwahl-Wortschatztest—Form B; HC, Healthy Control; SUD, Substance Use Disorder; FEP, First-Episode Psychosis; SCZ, Schizophrenia; DSST, digit symbol substitution task. Superscript numbers refer to the relevant reference number in the citations list.