Is opioid-induced hyperalgesia reversible? A study on active and former opioid addicts and drug naïve controls

Objective: Hyperalgesia has been observed in active opioid addicts (OAs). The aim of this study was to explore whether opioid-induced hyperalgesia (OJH) is a reversible phenomenon. Design: Observational study. Participants: The study included the following three groups of male subjects: 1) active addicts on heroin or methadone (OAs, n = 50); 2) former opioid addicts with at least 5 months of abstinence from drug use (FOAs, n = 43); and 3) drug naïve controls (C, n = 50). Interventions: All subjects were exposed to the cold pressor test (1°C). Main outcome measures: Cold pain threshold (latency to pain onset, seconds) and cold pain tolerance (latency to pain intolerability, seconds). Results: Mean ± standard deviation (SD) pain thresholds were 10.8 ± 7.7, 6.9 ± 3.9, and 6.8 ± 3.5 seconds for the OAs, FOAs, and C groups, respectively (analysis of variance [ANOVA], p = 0.002, 95% CI = 7.5-9.2). Mean ± SD pain tolerance levels were 30 ± 36.2, 64 ± 58.1, and 56.4 ± 51.4 seconds for the OAs, FOAs, and C groups, respectively (ANOVA, p < 0.001, 95% CI = 43-60.4). Post hoc analyses revealed significant changes between the OAs and the other two groups for both variables. Conclusions: It is suggested that altered pain perception in OAs is a reversible phenomenon that may require a long period of abstinence to reset, rather than being an individual long-term stable trait.