Opioids and abnormal pain perception: New evidence from a study of chronic opioid 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.