Evidence of validity and reliability of the Opiate Dosage Adequacy Scale (ODAS) in a sample of heroin addicted patients in buprenorphine/naloxone maintenance treatment

•The Opiate Dosage Adequacy Scale (ODAS) aims to measuring adequacy of opioid doses.•The ODAS factor structure revealed 4 factors (total variance explained 85.4%).•Adequate doses related to lower psychological distress, heroin use and dependence.•Results support ODAS validity and reliability in users of buprenorphine/naloxone. The Opiate Dosage Adequacy Scale (ODAS) is a clinical tool to individually measure the “adequacy” of opioid doses in patients on maintenance treatment. The aim of this paper is to provide evidence for the validity and reliability of the ODAS in a sample of patients in buprenorphine/naloxone (B/N) maintenance treatment. Cross-sectional study of a convenience sample of B/N-treated patients (n = 316) from four Autonomous Communities in Spain. Participants completed a battery of instruments to assess the following: buprenorphine dose adequacy; heroin dependence severity; psychological adjustment; and patient-desired adjustment of buprenorphine dose. Exploratory Factor Analysis identified four factors from the ODAS that together account for 85.4% of the total variance: “Heroin craving and use”; “Overmedication”; “Objective opiate withdrawal symptoms (OWS)” and ‘Subjective OWS’. Compared to patients with an “inadequate” B/N dose (ODAS), patients with “adequate” doses had less heroin use in the last week (0.01 vs. 0.40; t = −2.73; p