Gabapentin for Restoring GABA/Glutamate Homeostasis in Co-occurring Bipolar and Cannabis Use Disorders

Eligibility Criteria

• 1. Ages 18-65 years
• 2. Meet DSM-5 criteria for moderate or severe cannabis use disorder (CUD; within the past 3 months), provide a positive urine cannabinoid screen at baseline, and identify cannabis as the primary substance of abuse
• 3. Meet DSM-5 criteria for bipolar I or II disorder (BD) or Schizoaffective Disorder, Bipolar Type
• 4. Able to provide informed consent and read, understand, and accurately complete assessment instruments
• 5. Willing to commit to medication treatment and follow-up assessments
• 6. Prescribed daily use of at least one mood stabilizing medication (i.e., lithium, divalproex sodium, lamotrigine, carbamazepine, 2nd generation antipsychotic)
• 1. A primary psychiatric diagnosis other than BD (e.g., Schizophrenia)
• 2. Meet DSM-5 criteria for moderate or severe substance use disorder (other than cannabis or tobacco) within the past 60 days
• 3. Any uncontrolled neurological condition (e.g., epilepsy) that could confound the results of the study
• 4. Any history of brain injury with loss of consciousness greater than 5 minutes
• 5. Any history of mental retardation, dementia, or recent electroconvulsive therapy (in the past 3 months)
• 6. Any uncontrolled medical condition that may adversely affect the conduct of the study or jeopardize the safety of the participant
• 7. Hepatocellular disease as indicated by plasma levels of liver transaminases (aspartate transaminase, alanine transaminase) greater than 3 times the normal range
• 8. Renal insufficiency as indicated by plasma levels of creatinine greater than 2 times the normal range
• 9. Concomitant use of medications that could interfere with glutamatergic/GABAergic transmission (e.g., benzodiazepines, ceftriaxone, riluzole, memantine, ketamine, topiramate, vigabatrin), due to potential confounding effects
• 10. Concomitant use of opioid medications, benzodiazepines, barbiturates, chloral hydrate, sodium oxybate, or any other medication deemed to be hazardous if taken with gabapentin
• 11. Azelastine, orphenadrine, oxomemazine, paraldehyde, and thalidomide are generally contraindicated in patients taking gabapentin; as such, individuals taking these medications will be excluded
• 12. Women of childbearing potential who are pregnant, lactating, or refuse adequate forms of contraception
• 13. Current suicidal or homicidal risk
• 14. Baseline scores greater than 35 on the Montgomery-Asberg Depression Rating Scale or greater than 25 on the Young Mania Rating Scale
• 15. Has taken gabapentin in the last month or experienced adverse effects/allergic reaction (e.g., angioedema) from it at any time
• 16. Significant claustrophobia and/or past negative experiences with MRI
• 17. Presence of non-MRI safe materials in the body (e.g., ferrous metal implants, pacemaker)