Norwegian OAT Study Tracks Switching, LAIB Uptake, Illicit Use

Key Takeaways

• In this Norwegian outpatient OAT cohort followed for nearly 3 years, most patients receiving LAIB, sublingual buprenorphine, or methadone remained on their original medication.
• Medication switching affected 13.2% of patients; 15 of those switches were to slow-release oral morphine, and among switches between the 3 main MOUD groups, most were to LAIB.
• Negative outcomes were similar across medication groups, with 10% discontinuing treatment and 4% dying during follow-up.
• By 2025, the sublingual buprenorphine group reported fewer illicit substance-use problems than the LAIB and methadone groups, although the authors said differential attrition appeared to contribute.

For people with opioid use disorder in Norway, choosing, maintaining, and switching among methadone, sublingual buprenorphine, and long-acting injectable buprenorphine can shape long-term outpatient opioid agonist treatment. When all 3 options are available within one treatment system, an unresolved routine-care question is whether later illicit substance use tracks more closely with medication pathway or with a patient’s baseline clinical profile. That question was examined in one outpatient program in Agder County.

In the naturalistic follow-up study of medication transitions and illicit substance use during OAT, investigators tracked a complete outpatient opioid agonist treatment (OAT) cohort in Agder County, Norway, among 424 patients with opioid use disorder (OUD), using baseline medical-record data from May 2022 and follow-up data from February 2025. Baseline medications for opioid use disorder (MOUD) were long-acting injectable buprenorphine (LAIB) in 17%, sublingual buprenorphine in 50%, and methadone in 33%. Outcomes included medication transitions, discontinuation, mortality, and illicit substance use from the annual Norwegian OAT status report, which classified past-year use as never, occasional, or long-term before dichotomization for regression. The cohort design captured routine-care treatment pathways and a broad clinical substance-use measure.

During follow-up, 13.2% of patients switched medication, with transitions to slow-release oral morphine tracked separately from the 3 main MOUD groups, and among switches between the 3 main MOUD groups, most were to LAIB. The LAIB share rose from 17% to 22%, about 7 in 10 patients remained on their original medication, and negative outcomes included 10% discontinuing treatment and 4% dying, with no significant difference between medication groups. Overall, medication pathways appeared fairly stable within this outpatient program.

Illicit substance use did not significantly differ across medication groups at baseline, but by 2025 the sublingual buprenorphine group showed fewer reported problems than the LAIB and methadone groups. The authors said that follow-up profile may have been partly shaped by differential attrition, with more severe baseline cases appearing more likely to exit or transition out of the sublingual buprenorphine group. In the adjusted predictor analysis for illicit substance use at follow-up, baseline illicit substance use was the strongest predictor of 2025 illicit substance use (OR 6.10, 95% CI 3.83-9.71, p < 0.001). Using 2025 medication-group membership in the model, the sublingual buprenorphine group had lower odds than methadone, whereas LAIB did not significantly differ from methadone.

Because medication assignment was naturalistic rather than randomized, between-group differences may reflect clinical selection and patient preference as well as medication pathway. The illicit substance-use measure was a coarse annual clinical-report variable based on patient self-assessment and was dichotomized for regression, so it functions as an indicative proxy rather than a substance-specific endpoint. The 2025 group comparisons were cross-sectional, the long interval between registration points may have missed interim medication changes, and dose information was unavailable.

Within this single-center Norwegian OAT cohort, baseline substance-use severity appeared to matter more for 2025 illicit substance use than 2025 medication-group membership. LAIB uptake increased modestly, and attrition outcomes were similar across medication groups. These findings are observational associations rather than causal comparisons among medications.

Clinician Questions

How was illicit substance use measured in this Norwegian OAT cohort?

Illicit substance use came from the annual Norwegian OAT status report and covered the preceding year, using 3 categories: never, occasional, or long-term use. The entry could be completed by the clinician with patient involvement, and the regression analysis later dichotomized the measure into use versus non-use. The measure captured illegal substances broadly rather than specific drugs.

Which patients were included in this follow-up of methadone, sublingual buprenorphine, and LAIB?

The follow-up included all patients with opioid use disorder receiving outpatient OAT at one clinic in Agder County, Norway, who were already in treatment at the May 2022 baseline. Patients newly enrolled between the 2 registration points were not added, so the findings reflect a fixed routine-care cohort rather than incident starters across the interval.

Why did the sublingual buprenorphine group look more favorable for illicit substance use in 2025?

The 2025 comparison was cross-sectional, and the remaining participants in the sublingual buprenorphine group had less severe baseline substance-use profiles than those who exited or switched. The authors said differential attrition appeared to contribute to the more favorable follow-up profile, so the pattern should not be read as a clean medication effect.