The Blinded-Dose Purchase Task
At the end of each session, participants in the cocaine and methamphetamine groups completed a blinded purchasing task for hypothetical capsules of that morning’s randomized dose (oral placebo, 125 mg/70 kg, or 250 mg/70 kg for cocaine hydrochloride; oral placebo, 20 mg, or 40 mg for d-methamphetamine hydrochloride). The alcohol group completed the Blinded-Dose Purchase Task for drinks associated with either the placebo or 1.0 g/kg dose of ethyl alcohol. In these tasks, participants indicated how many units of that day’s dose they would purchase to consume over the next month across the following 10 escalating price points: $0.01, $0.03, $0.30, $1, $3, $10, $30, $100, $300, and $1000. Price points were presented on separate pages, and were selected primarily to assess the range of purchasing across numerous prices as in previous studies. Participants read the following scenario prior to beginning the purchase task:Imagine that you have finished the study and will spend the next month in your usual home environment. Also imagine that you have the chance to buy today’s drug dose for your own personal use within the next month. Please consider what you have received today to be a single dose. You can buy as many doses as you like, but you cannot sell, trade, or give them away, and you cannot save them for more than a month. Other than the fact that the doses are for your own use within the next month, there is no limit to the number of doses you can buy. Please do not buy more than you will use...Participants then responded to the following question for each of the price points: If today’s drug dose costs [X] each, how many drug doses would you buy to use in the next month?