Abstract Background Approximately 3% of people receiving opioid substitution therapy (OST) in the UK manage to achieve abstinence from prescribed and illicit drugs within three years of commencing treatment. Involvement of families and wider social networks in supporting psychological treatment may be an effective strategy in facilitating recovery, and this pilot study aimed to evaluate the impact of a social network-focused intervention for patients receiving OST. Methods A two-site, open feasibility trial randomised patients receiving OST for at least 12 months but still reporting illicit opiate use in the past 28 days to one of three treatments: 1) treatment as usual (TAU), 2) Brief Social Behaviour and Network Therapy (B-SBNT) + TAU, or 3) Personal Goal Setting (PGS) + TAU. The two active interventions consisted of 4 sessions. There were 3 aims: 1) test the feasibility of recruiting OST patients to a trial of B-SBNT, and following them up over 12 months; 2) test the feasibility of training clinicians to deliver B-SBNT; 3) test whether B-SBNT reduces heroin use 3 and 12 months after treatment, and to explore potential mediating factors. The primary outcome for aim 3 was number of days of heroin use in the past month, and a range of secondary outcome measures were specified in advance (level of drug dependence, mental health, social satisfaction, therapist rapport, treatment satisfaction, social network size and support). Results A total of 83 participants were randomised, and 70 (84%) were followed-up at 12 months. Fidelity analysis of showed that B-SBNT sessions were clearly distinguishable from PGS and TAU sessions, suggesting it was possible to train clinical staff to an adequate level of competence. No significant differences were found between the 3 intervention arms in the primary or secondary outcome measures. Attendance at psychosocial treatment intervention sessions was low across all three arms (44% overall). Conclusions Patients receiving OST can be recruited into a trial of a social network-based intervention, but poor attendance at treatment sessions makes it uncertain whether an adequate dose of treatment was delivered. In order to achieve the benefits of psychosocial interventions, further work is needed to overcome poor engagement. Trial registration ISRCTN Trial Registration Number: ISRCTN22608399 . Date of registration: 27/04/2012. Date of first randomisation: 14/08/2012.