大麻は安いのか？ 大麻の需要と実験室での購入との相関関係

The typical Marijuana Purchase Task (MPT) assesses hypothetical demand (i.e. relative reinforcing value) for cannabis across escalating prices. Cannabis demand has been related to use frequency, craving, cannabis use disorder symptoms and cue-exposure response, among other outcomes. This study assessed MPT performance for hypothetical consumption in relation to in vivo behavior in the laboratory wherein rewards were actualized.

Individuals endorsing cannabis use at least twice weekly (n = 92) participated in a laboratory cannabis self-administration study. Participants completed MPTs for Hypothetical and Actual cannabis. One trial (i.e. amount purchased at specified price) was randomly selected from the Actual MPT and participants with non-zero value trials (n = 81) were permitted to smoke up to that amount during a 1-hour session in the laboratory.

Bivariate Pearson correlations demonstrated that cannabis consumption preferences were highly similar across the Hypothetical and Actual MPT at the price (rs = 0.45-0.81) and index (rs = 0.46-0.81) level. However, mean O_max (i.e. maximum expenditure), P_max (i.e. price at maximum expenditure) and breakpoint (i.e. price suppressing consumption to zero), were statistically significantly higher (ds = 0.47-0.51), and elasticity (i.e. consumption decline rate relative to price increase) was statistically significantly lower (d = -0.58) for the Actual MPT compared with the Hypothetical MPT; this was also evident at certain price points. Self-reported anticipated consumption was statistically significantly related to the amount of cannabis smoked during self-administration (R² = 0.66; P < 0.001) and was not moderated by price of the randomly selected trial.

High correspondence between Hypothetical and Actual Marijuana Purchase Task (MPT) performance in a laboratory setting suggests that hypothetical versions of the MPT may be broadly valid measures of cannabis demand. The robust relationship between anticipated consumption and actual cannabis quantity smoked in the laboratory suggests individual self-report accurately predicts subsequent self-administration, further supporting the construct validity of hypothetical MPTs.