Risky Decision Making in Methamphetamine Users: The Role of Opioid Blockade

Study Overview
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Brief Summary
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The purpose of this protocol is to learn more about impulsive decision making in people who use methamphetamines. The investigators would like to know if a medication called naltrexone changes how people make decisions. The investigators would also like to know whether changes in decision making can be observed by MRI (magnetic resonance imaging). The research is conducted in Portland, OR.

Official Title
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Risky Decision Making in Methamphetamine Users: The Role of Opioid Blockade

Conditions
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HIV, Methamphetamine Abuse

Intervention / Treatment
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* Drug: Extended release naltrexone
* Drug: Placebo


Participation Criteria
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Eligibility Criteria
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Summary Inclusion Criteria: Diagnostic and Statistical Manual (DSM)-IV Methamphetamine Dependence Deemed healthy enough to participate by study physician Age 18-55 Right handed English-speaking Summary Exclusion Criteria: Current opioid use in the last 30 days; opioid abuse or dependence within past 5 years Pregnancy MRI contraindications (e.g. metal in head). The research is conducted in Portland, OR.

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 55 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Other
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Triple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Extended release naltrexone<br>One dose of intramuscular injection of 380mg extended-release naltrexone. | Drug: Extended release naltrexone<br> <br> * Other names: Vivitrol;|
| Placebo Comparator: Placebo<br>One dose of intramuscular injection of placebo. | Drug: Placebo<br> <br> |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Discounting Tasks: Sexual Probability Discounting (SexPD) | In the SexPD task, subjects are asked to choose between having sex with a more appealing partner with a varying chance of having a sexually transmitted infection (STI) or a less appealing partner with no STI. A hyperbolic decay model was used to calculate h, a free parameter that indexes the rate of probabilistic discounting. Smaller h values indicate a preference for probabilistic (i.e., riskier) outcomes. To normalize the data, the natural log of h values were calculated and reported here. | 28 days post drug intervention | 
| Discounting Tasks: Standard Delay Discounting (DD) | Monetary delay discounting task consisted of choosing between a larger, delayed and a smaller, immediate reward. A hyperbolic decay model was used to calculate k, a free parameter that indexes the rate of delay discounting. As k values are typically skewed across subjects, the distribution of k was normalized by using a natural log transformation. The normalized values are reported here. If k typically ranges between 0.5 and 10^-5, then the natural log of k will range between -0.69 and -11.5. Larger normalized k values indicate a preference for smaller sooner outcomes (i.e., more impulsive decision-making). | 28 days post drug intervention | 
| Barrat Impulsiveness Scale (BIS) | The Barrat Impulsiveness Scale (BIS) is a 30 item questionnaire to measure a persons impulsiveness. Items are answered on a 4-point scale and scored 1-4 then summed across responses. Total scores range from 30-120 with a higher summed score indicating higher impulsivity. | 28 days post drug intervention | 
| Risk Assessment Battery (RAB) | The Risk Assessment Battery (RAB) is a 26 question self-administered assessment focusing on drug use, injection and sexual risk during the past 30 days. Three composite HIV risk scores (drug, sex, and total score) are calculated. The questions have different numbers of items, and scores for a single question can range from 0 to 7, with higher values reflecting more instances of risk behavior. The drug risk score has a range of 0 to 22 and is calculated from 8 questions that address recent substance use, including frequency, needle sharing, and cleaning of the works. 9 questions are used to calculate a sex risk score that has a range of 0 to 18, and these questions address the frequency and types of sexual behavior, HIV status of sexual partners, and type of protection that was used (if any). Total score is calculated by adding drug and sex scores and dividing by 40, the maximum score possible, and ranges from 0 to 40 where higher scores indicate greater risk behavior. | 28 days post drug intervention | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Methamphetamine Use | Participants were asked How many days in the past 30 days did you use methamphetamine?. This is a self-report measure. | 28 days post drug intervention |