Pain Responses in Patients on Long-Term Opioid Therapy for Chronic Pain

a. Inclusion/exclusion criteria Inclusion Criteria for the group with chronic pain on chronic treatment with opioids: 1. Subject has chronic pain and is on stable chronic opioid treatment (morphine, fentanyl, oxycodone, methadone, hydromorphone, hydrocodone) for chronic pain for at least one month. We consider stable treatment if no change in the type and amount of daily opioid treatment for one month. Only patients with minimal daily opioid dose of at least 30 mg morphine equianalgesic dose will be included. 2. Subject is age 18 to 65 years. Inclusion Criteria for the group with chronic pain on chronic treatment with non-opioids (currently not recruiting): 1. Subject has pain and is on stable chronic non-opioid treatment for chronic pain for at least one month. 2. Subject is age 18 to 65 years. Inclusion Criteria for the group of opioid-naive healthy volunteers without chronic pain (currently not recruiting): 1. Subject is opioid naive meaning he/she did not receive chronic opioid treatment in the past or present, and did not receive acute treatment with opioids in the last 1 month 2. Subject does not have pain 3. Subject is age 18 to 65 years. Exclusion Criteria for all groups: 1. Subject has lost tactile sensation in the sites for QST testing (upper extremities) 2. Subject has scar tissue or acute injury in the skin areas for QST testing (upper extremities) 3. Subject has neurological disease or a medical condition causing peripheral polyneuropathy and sensory changes (including but not limited to diabetes, alcoholism, AIDS, thyroid disease, liver or kidney disorders). It is the presence of neuropathy, not the causative disease itself, that is the exclusion criteria. 4. Subject had recent therapy that may influence QST results, e.g., neuroablative procedure involving upper extremities within six-months; peripheral neurolytic block within two-months; injection therapy for pain within four-weeks; sympathetic block within six months. 5. Subject has litigation pending relative to their chronic pain. 6. Subject has major psychiatric disorder (major depression disorder; bipolar disorder; schizophrenia; anxiety disorder; psychotic disorders; eating disorders; alcohol or drug dependence; attention deficit hyperactivity disorder); any known history of these conditions will exclude participation. 7. Subject has used illicit drugs within past 6 months. 8. Subject is pregnant