Opioids and abnormal pain perception: New evidence from a study of chronic oploid addicts and healthy subjects

Recent evidence reported on increased pain sensitivity in animals following parenteral opioid administration and in humans subsequent to intravenously of short-acting opioids and possibly in drug addicts. The aims of the present study were to explore the possibilities that (1) pain perception is altered in chronic opioid addicts (OAs); (2) if indeed so, the cessation of opioid consumption resets their altered pain perception. Sixty heroin or methadone OAs who attended a 4-week inpatient detoxification program were exposed to the cold pressor test (CPT) upon entrance to the program, at 7 and 28 days subsequent to the cessation of opioid consumption (verified by repeated urine toxicology tests). Latency of pain onset (s), pain intensity (0-100 VAS), and tolerance (time for hand withdrawal) in response to the CPT were measured. In comparison with 70 healthy controls, the OAs demonstrated prolonged latency (6.6 +/- 3.5 s versus 10.9 +/- 7.7 s; p < 0.0001); decreased VAS (74 16 versus 55 20; p < 0.0001); shorter tolerance (56.4 +/- 51.3 s versus 31.7 +/- 40.7 s; p = 0.001). No differences between the three time points in any of the three measures were detected in the OAs. The results provide further evidence of opioid-induced hyperalgesia in the OA population, as manifested by their quicker hand withdrawal. In addition, it appears that detoxification from opioids does not reset pain perception for at least 1 month. (c) 2005 Elsevier Ireland Ltd. All rights reserved.