Table 1.

Characteristics of the human studies focused on the effect of cannabis on cognition

	Sample	Characteristics of cannabis exposure	IV(s)	DV(s)	Design	Risk, resilience, or null	Effect strength/quality
Meier et al. [29]	N = 1037; 52% male	Dependence diagnosis or weekly cannabis use before age 18 or after age 18	Number of dependence diagnoses throughout study (dependence @ 1 wave, @ 2 waves, or @ 3 + waves) BY age of first dependence diagnosis (before age 18 or after age 18)	Change in IQ (IQ post-cannabis initiation @ age 38 minus average IQ pre-cannabis initiation @ age 7, 9, 11, 13) 7 participants initiated before age 13, so their pre-cannabis and post-cannabis IQ was adjusted accordingly	Cannabis assessments @ ages 5, 7, 9, 11, 13, 15, 18, 21, 26, 32, 38 (Diagnostic Interview Schedule or weekly cannabis use frequency) Neuropsychological assessments @ ages 7, 9, 11, 13, 38 (Wechsler Intelligence Scale for Children-Revised or for Adults-IV)	Null for dependence @ 1 or @ 2 waves BY age of first diagnosis Risk for dependence @ 3 + waves BY age of first dependence diagnosis Interpretation For those diagnosed with dependence @ 3 + waves, IQ declined 0.55 SD units more among those that first met dependence before age 18 compared to those that first met dependence after age 18; results replicated when using weekly cannabis use before or after age 18 as the IV, instead of a diagnosis of dependence	Medium to large/moderate
Scott et al. [30]	N = 4568; 44% male	Three groups: (1) no history of use; (2) use “1–2 times per week” or less the past year; (3) “3–4 times per week” or “Daily or Almost Daily” use over the past year	Age (14–21) BY cannabis group (3 levels) BY cognitive domains (4 levels)	Cognitive function (executive control, memory, complex cognition, social cognition) assessed through the Penn Computerized Neurocognitive Battery	Participants were drawn from a sample of 50,293 adolescents and young adults who were part of the Philadelphia Neurodevelopment Cohort	Null for age BY cannabis group on memory, complex cognition, and social cognition Risk for age BY cannabis group on executive control Interpretation Daily or almost daily users performed worse in executive control than non-users at younger but not older ages	Small/moderate
Lee et al. [31]	N = 269; 55% male adults; 88% male teens	A mean of 10.7 and 22.2 on past 30-day cannabis use for adolescents and adults, respectively	Age [(165 adolescents (12–18 years old) vs. 104 adults (18 and up years old))] BY time point (intake vs. treatment) BY type of discounting (cannabis vs. money)	Delay discounting rates to cannabis and money paradigms	Participants whom were part of an outpatient treatment program completed questionnaires and delay discounting tasks before and after treatment	Null for age BY time point BY type of discounting Risk for age BY time point Interpretation Adolescents had smaller decreases in delay discounting for cannabis and money pre to post-treatment than adults	Not presented/weak
Albertella et al. [32]	N = 124; 42% male	Two groups: (1) used cannabis less than once per week or no use in the past 6 months; (2) used once a week or more often	Age (14 or 15*–24) BY cannabis group (2 levels) *Note: different age ranges 14–24 and 15–24 were mentioned in text	Negative priming (location-based negative priming task)	The study was entirely online and programs were run through Inquisit software	Risk for age BY cannabis use on negative priming for weekly users Interpretation Young and weekly users exhibited reduced negative priming compared with older and frequent users Null for age BY cannabis use on negative priming for less than weekly users	Small to medium/weak
Mokrysz et al. [39]	N = 40; 100% male	Medicinal cannabis—sativa strain (THC 12%) and placebo (THC < 0.3%) A mean of 10.58 and 7.94 days per month for adolescents and adults, respectively	Age [(20 male adolescents (16–17 years old) vs. 20 male adults (24–28 years old))] BY cannabis treatment (placebo vs. active)	Cognitive disorganization (VAS), alertness (VAS), craving (VAS), spatial memory accuracy and reaction time(N-Back), prose recall (subtest of Rivermead Behavioural Memory test battery), inhibitory control accuracy and reaction time (Stop Signal)	Placebo-controlled, double-blind cross-over design with vaporized placebo and vaporized active cannabis (12% THC) 24-h abstinence period before testing (not biologically verified)	Null for age BY cannabis treatment on spatial memory accuracy Resilience for age BY cannabis treatment alertness, for cognitive disorganization, for spatial memory reaction time, and for immediate and delay prose recall Interpretation Adolescents showed increased alertness, spatial memory reaction time, and immediate and delayed prose recall as well as decreased cognitive disorganization following intoxication compared to placebo Null for age BY cannabis treatment on inhibitory control reaction time Risk for age BY cannabis treatment craving and inhibitory control Interpretation Adolescents showed increased craving pre to post-intoxication whereas adults decreased. Adolescents exhibited reduced inhibitory control during intoxication whereas adults were unaffected	Small to medium/moderate
Padovano et al. [40]	N = 85; 52.8% male	Overall sample cannabis use was 21 days per month and 0.65 g per day of use	Age continuously (15–24 years old) BY report type (before cannabis, after cannabis, non-use)	Craving, alertness (VAS)	Ecological momentary assessment with several prompts per day across 14 days. The report types were categorized as: a non-use assessment; end-cannabis assessment (after cannabis use, no later than 3 h post-cannabis); begin-cannabis assessment (before cannabis use)	Null for age BY report type on craving Null for age BY report type on sedation Resilience for age BY report type on alertness from pre to post cannabis use Interpretation Age was negatively associated with change in alertness pre to post cannabis use, such that older individuals were less alert after cannabis use	Small/moderate

IV(s) independent variables, DV(s) dependent variables; VAS Visual Analogue Scale; IQ Full Scale Intellectual Quotient. Numbers in brackets correspond to the studies placement in the reference section. We determined adolescents’ risk, resilience, or null classification based on the statistical tests. The risk, resilience, or null interpretation is from the adolescent’s perspective. Only the analyses that statistically explored age as a moderator for cannabis and cognition were reported. For the DV(s) listed, the measure used to assess this cognitive domain is listed in parentheses. The effect strength was determined through standard deviation units, standardized beta-coefficients, and/or official effect sizes presented within the study’s text, with values of 0.20, 0.50, and 0.80 reflecting small, medium, and large effects, respectively. Some studies were missing this information and are, therefore, reported as “not presented”