Overview Effect of Guanfacine on Opioid-induced Hyperalgesia (OIH) and Tolerance Status: Active, not recruiting Trial end date: 2021-12-01 Target enrollment: Participant gender: Summary Dual medication (guanfacine and morphine) as a standard treatment for chronic pain. Phase: Phase 4 Details Lead Sponsor: Massachusetts General HospitalCollaborators: National Institute on Drug Abuse (NIDA)National Institutes of Health (NIH)Treatments: GuanfacineMorphinePolystyrene sulfonic acid