Further validation of a marijuana purchase task

Abstract

Background A valid measure of the relative economic value of marijuana is needed to characterize individual variation in the drug’s reinforcing value and inform evolving national marijuana policy. Relative drug value (demand) can be measured via purchase tasks, and demand for alcohol and cigarettes has been associated with craving, dependence, and treatment response. This study examined marijuana demand with a marijuana purchase task (MPT). Methods The 22-item self-report MPT was administered to 99 frequent marijuana users (37.4% female, 71.5% marijuana use days, 15.2% cannabis dependent). Results Pearson correlations indicated a negative relationship between intensity (free consumption) and age of initiation of regular use (r=−0.34, p<0.001), and positive associations with use days (r=0.26, p<0.05) and subjective craving (r=0.43, p<0.001). Omax (maximum expenditure) was positively associated with use days (r=0.29, p<0.01) and subjective craving (r=0.27, p<0.01). Income was not associated with demand. An exponential demand model provided an excellent fit to the data across users (R2=0.99). Group comparisons based on presence or absence of DSM-IV cannabis dependence symptoms revealed that users with any dependence symptoms showed significantly higher intensity of demand and more inelastic demand, reflecting greater insensitivity to price increases. Conclusions These results provide support for construct validity of the MPT, indicating its sensitivity to marijuana demand as a function of increasing cost, and its ability to differentiate between users with and without dependence symptoms. The MPT may denote abuse liability and is a valuable addition to the behavioral economic literature. Potential applications to marijuana pricing and tax policy are discussed.

Interrelationships between marijuana demand and discounting of delayed rewards: Convergence in behavioral economic methods

“…Exclusion criteria were: intent to quit or receive treatment for cannabis abuse, positive urine toxicology test result for drugs other than marijuana, pregnancy, nursing, past month affective or panic disorder, psychotic or suicidal state assessed by psychiatric interview, contraindicated medical issues assessed by physical exam, body mass index > 30, and smoking more than 20 tobacco cigarettes per day. Five participants showed evidence of low effort on the MPT (e.g., inconsistent responding across prices) and were excluded from subsequent analysis (Aston et al, 2015). The final sample included 83 participants (35% female).…”

“…For example, indices of tobacco cigarette demand have been linked with increased nicotine dependence (Chase et al, 2013; MacKillop et al, 2008; Murphy et al, 2011), and alcohol demand metrics have been significantly related to alcohol problem severity and level of alcohol consumption (MacKillop et al, 2010; Murphy et al, 2009; Murphy and MacKillop, 2006). Furthermore, indices of marijuana demand have been related to cannabis dependence (CD) symptom count and self-reported marijuana craving (Aston et al, 2015), as well as level of use (Aston et al, 2015; Collins et al, 2014) and cue-elicited craving (Metrik et al, 2016). …”

Cue-elicited increases in incentive salience for marijuana: Craving, demand, and attentional bias

“…The median annual family income bracket of participants was $60,000-69,000. Five participants showed inconsistent responding on the marijuana purchase task (MPT) and were excluded from MPT analyses (Amlung et al, 2012; Aston et al, 2015). …”

“…The MPT assesses how many marijuana hits one would smoke right now at 22 prices ($0 to $10 per hit; see Aston et al, 2015 for exact prices) if the marijuana available was of average quality and strength, was available only from this source, could not be stockpiled (had to be consumed), and if no marijuana or drugs were used prior to making choices on this task. Task instructions specified that there were 10 hits of marijuana in a joint and there was no limit on hits or joints (1 joint=1/32 nd of an ounce=0.9 grams).…”

“…Analogous to behavioral operant progressive-ratio schedules, purchase tasks offer an efficient mode of evaluating drug demand. Purchase tasks have been psychometrically validated for marijuana (Aston et al, 2015; Collins et al, 2014), alcohol (Murphy and MacKillop, 2006), and tobacco consumption (Jacobs and Bickel, 1999; MacKillop et al, 2008). Moreover, state purchase tasks intended to measure phasic changes in relative drug value have been applied in the context of CR with alcohol (Amlung et al, 2012; MacKillop et al, 2010) and tobacco (Acker and MacKillop, 2013; Hitsman et al, 2008; MacKillop et al, 2012).…”