["Addiction, EarlyView. ", "\nAbstract\n\nBackground and aims\nFew studies have examined multiple domains of sleep deficiency among patients receiving methadone treatment (MT). This study investigated sleep deficiency classes and their associations with demographics, clinical characteristics and one‐year treatment outcomes among patients receiving MT.\n\n\nDesign\nLongitudinal study using patient‐completed questionnaires on demographics, sleep, pain interference with sleep and psychological symptoms in August 2023. We used latent class analysis to group patients into sleep deficiency classes and employed multinomial logistic regression to investigate their demographic and clinical correlates. Treatment continuity and urine toxicology results over the subsequent year were analyzed in August 2024.\n\n\nSetting\nA not‐for‐profit federally certified opioid treatment program in Connecticut, USA.\n\n\nParticipants\n1237 patients receiving MT.\n\n\nMeasurements\nSleep questionnaires included the Pittsburgh Sleep Quality Index, Insomnia Severity Index, Epworth Sleepiness Scale, Brief Index of Sleep Control, STOP questionnaire and the first two items from the Cambridge‐Hopkins Restless Legs Syndrome Questionnaire. Urine toxicology results and treatment continuity were extracted from the medical chart.\n\n\nFindings\nWe identified four classes. Class I (28.0%): normal sleep/no sleep deficiency. Class II (24.8%): late sleep with increased risk for obstructive sleep apnea and restless legs syndrome. Class III (20.5%): poor sleep quality with short and late sleep. Class IV (26.6%): severe sleep deficiency. Compared with Class I, participants in Classes II–IV had statistically significantly higher odds of reporting psychological symptoms [Class II adjusted odds ratio (aOR) = 1.41, 95% confidence interval (CI) = 1.10–1.81; Class III aOR = 1.58, 95% CI = 1.23–2.03; Class IV aOR = 2.21, 95% CI = 1.72–2.84] and pain interference with sleep (for three or more days per week: Class II aOR = 5.52, 95% CI = 2.93–10.38; Class III aOR = 5.04, 95% CI = 2.62–9.69; Class IV aOR = 13.16, 95% CI = 6.98–24.84). Over the subsequent year, compared with Class I, participants in Class III had statistically significantly higher rates of positive urine toxicology results for benzodiazepines, while participants in Class IV had statistically significantly higher rates of positive urine toxicology results for fentanyl and benzodiazepines. Treatment continuity did not differ across the four classes after one year following baseline.\n\n\nConclusions\nVarieties of sleep deficiency compared with normal sleep appear to be associated with more severe psychological symptoms and pain interference with sleep among patients receiving methadone treatment and may serve as risk factors for substance use.\n\n"]