Silverman 2015b.

Study characteristics
Methods	Study design: cluster RCT Study grouping: parallel group Allocation concealment: not specified Randomisation method: throughout 18 MT treatment sessions, the researcher cluster randomised consumers into experimental or control conditions by session. The numbers 1–18 were randomised into 2 groups, and each group was assigned to either the experimental or control condition.
Participants	Baseline characteristics MT + SC Gender male: 27 (52.9%) Age: 42.35 years Sample size: 51 SC (wait‐list control) Gender male: 30 (56.6%) Age: 40.87 years Sample size: 53 Overall Gender male: 57 (54.8%) Age: 41.61 years Sample size: 104 Inclusion criteria: inpatient on detoxification unit; ability to read English Exclusion criteria: none mentioned Pretreatment: no significant differences between groups in regard to: number of consumers taking part in each session who volunteered to be research participants; total number of consumers in each session; participants' age; number of times had been in rehabilitation/detoxification facility; gender; race/ethnicity; drug of choice. Confirmation of population eligibility (from study author): author confirmed that participants had diagnosis of SUD.
Interventions	Intervention characteristics MT + SC Description: MT lyric analysis group session focused on treatment motivation and relapse prevention led by a board‐certified music therapist. Therapeutic techniques were manualised using the functional CBT manual by Cather 2005. Session length: approximately 45 minutes Frequency: single session Duration of treatment: single session SC (wait‐list control) Description: wait‐list control Session length: not applicable Frequency: not applicable Duration of treatment: not applicable
Outcomes	Motivation for treatment – the Texas Christian University Treatment Motivation Scale – CESI Outcome type: continuous outcome Reporting: partially reported Scale: 5‐point Likert‐type scale for each item Direction: higher is better Data value: endpoint Notes: higher scores on the CESI indicate greater motivation for change, and the 4 subscales can be added together for a total motivation score. We only used the total motivation score, though author also reports subscales. Unable to determine range of the CESI from existing literature.
Identification	Sponsorship source: none Country: USA Setting: inpatient detoxification unit Author's name: Michael J Silverman Institution: University of Minnesota Email: silvermj@umn.edu Declarations of interest: no conflicts of interest reported.
Notes	Email (13 September 2017) from author confirmed that participants met criteria for SUD.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Judgement comment: throughout 18 MT treatment sessions, the researcher cluster randomised participants into experimental or control conditions by session. The numbers 1–18 were randomised into 2 groups, and each group was assigned to either the experimental or control condition.
Allocation concealment (selection bias)	Unclear risk	Judgement comment: insufficient information about allocation concealment to permit judgement.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Judgement comment: missing outcome data balanced in numbers across intervention groups, with similar reasons for missing data across groups. Reasons for missing outcome data unlikely to be related to true outcome.
Selective reporting (reporting bias)	Low risk	Judgement comment: no selective outcome reporting.
Blinding of participants and providers (performance bias) (subjective outcomes)	Low risk	Judgement comment: not possible to blind participants and providers to MT intervention.
Blinding of outcome assessor (detection bias) (subjective outcomes)	Unclear risk	Judgement comment: not possible to blind outcome assessor for self‐report outcomes, though measurement not likely to be influenced differentially between groups.