Statistical analyses
depression, anxiety
DISORDER, DELETION
In order to investigate the effects of CBD on anandamide levels, linear mixed-effects models were used due to the ability to incorporate missing data into analysis via maximum likelihood estimation, in an intention-to-treat analysis. Anandamide level was the dependent variable. CBD (placebo, 400 mg/day, 800 mg/day; reference category: placebo) and time (day 0, day 14 and day 28; reference category: day 0) were added as predictor variables. Because this was a clinical trial for the treatment of cannabis use disorder and changes in cannabis use could potentially influence anandamide levels, models were run both unadjusted and adjusted for cannabis use (urinary THC:COOH/creatinine ratios). CBD, time and their interaction were modelled as fixed effects. In adjusted models, cannabis use (measured as THC:COOH-creatinine ratios) was fitted as a covariate. Participant was fitted as a random intercept. The covariance structure was selected as first-order autoregressive as this provided the greatest model fit and accounted for the likelihood that measurements taken closer in time would be more strongly correlated. Significance was assessed according to an alpha level of 0.05. Models were conducted on an intention-to-treat basis under the assumption that missing data were at random. A total of 70 participants were included in the analysis. Datapoints of anandamide were missing in 21 instances. Additionally, in 11 instances, levels of anandamide were below the limit of quantification. These data were coded as missing allowing them to be estimated via maximum likelihood estimation without listwise deletion.The original data produced a model with residuals that deviated from normality (skewness = 2.16, excess kurtosis = 6.68). Following recommendations by Tabachnick and Fidell [In order to investigate the extent to which changes in anandamide levels were associated with changes in anxiety, depression, cannabis use or withdrawal, Spearman’s rank-order correlation coefficients were calculated. This was done using the winsorised data. Correlations were stratified by CBD dosage and were conducted between changes in anandamide levels (from day 0 to 28) and changes in anxiety/depression/cannabis use (as THC:COOH-creatinine ratios or as days per week abstinent from cannabis)/cannabis withdrawal (from day 0 to 28). Significance was assessed using Bonferroni-adjusted alpha levels of 0.0125 (0.05/4). Bias corrected and accelerated bootstrapped confidence intervals of correlation coefficients were calculated based on 10,000 samples. All analyses were conducted using IBM SPSS version 27.