This study will test whether 42 days of cannabis abstinence, compared to continued cannabis use, is associated with improvements in cognition and psychiatric disorder symptoms. Identical twins, who are concordant on cannabis use, will be experimentally-manipulated to be discordant for 42 days. Each twin, within a twin pair, will be randomly assigned to either the contingency management condition, incentive-based protocol to promote cannabis abstinence, or control condition, no changes in cannabis use requested.

The proposed project is a randomized controlled trial to compare cognition and psychiatric disorder symptoms between monozygotic (MZ) twin pairs, who are concordant on frequency of cannabis use. Each twin, within the twin pair, will be randomly assigned to either contingency management (CM), monetary incentives provided to reinforce cannabis abstinence, or control, no changes in cannabis use required or reinforced. Participants in the CM condition will receive an increasing schedule of payments at each visit reinforcing continued cannabis abstinence. All participants will receive increases in the payment schedule for attendance of each subsequent assessment. Participants will be assessed on measures of cognition including attention, memory, and processing speed as well as anxiety, depression, and ADHD symptoms. In addition, at each visit participants will complete a qualitative and quantitative drug test. The qualitative drug test will be used to determine if new cannabis use has occurred since the last visit, and will determine if the participant receives payment for abstinence. The investigators will also use previously collected genotype for each participant.

The first aim of this study is to characterize cognitive recovery, across all potential cognitive domains, using an experimental manipulation to achieve discordance between MZ twins on cannabis use. The hypothesis for the first aim is that the abstinent group will have greater improvements in memory and processing speed compared to controls. However, there will not be any group differences between the abstinent group and the control group on attention, language, and executive function performance. The second aim of the proposed project is to characterize psychiatric disorder symptoms by comparing psychiatric disorder symptom changes among the cannabis abstaining twin to their cannabis using co-twin across 42 days. The abstinent group will endorse more psychiatric symptoms during the withdrawal period (up to 14 days) but will endorse fewer psychiatric symptoms at day 28 and 42 compared to the control group. The third aim (exploratory) of the proposed project is to examine how genetic risk for psychiatric disorders interacts with environment (i.e., cannabis abstinence versus continued use) to influence cognitive functioning. The hypothesis for aim 3 is that anxiety, depression, and ADHD polygenic scores will be more strongly associated with cognitive outcomes in the control group compared to the abstinent group.

Inclusion Criteria:

1. Monozygotic (MZ) twin pair, in which both twins are willing to participate
2. MZ twin pair must be concordant in their frequency of cannabis use (+/- 2 days)
3. Cannabis use at least 1x per week on most weeks
4. Cannabis use in the past 7 days at the baseline visit
5. Positive qualitative urine toxicology at baseline for THC
6. Located within the state of Colorado

Exclusion Criteria:

1) Discordance in the twin pairs on a significant, adverse experience, like traumatic brain injury.

In accordance with NIH data sharing policies, data produced from this project will be made available to ensure timely translation of research results to improve human health. The investigators believe there is a possibility of deductive disclosure of subjects with unusual characteristics, even though all identifiers would be removed prior to release for sharing. Thus, the investigators will make the data and associated documentation available to users only under a specific data-sharing agreement that requires: (1) a commitment to using the data only for research purposes and not to identify any individual participant; (2) a commitment to securing the data using appropriate computer technology; and (3) a commitment to destroying or returning the data after analyses are completed.