Introduction

Quitlines help smokers to stop but few studies have explored how behavioural and medicinal interventions can be optimally delivered via this route.1 One of these was the PORTSSS trial, which found that offering free nicotine replacement therapy (NRT) vouchers did not increase cessation rates compared with no offer.2 It also found that a ‘proactive’, more intensive call regime from/to clients did not improve cessation rates over ‘usual care’. Was it possible that participants who did not receive a voucher for NRT sought out and used other forms of cessation support, which minimised any effect of receiving the NRT voucher? Use of ‘non-trial’ support varied across PORTSSS trial intervention groups and, in this analysis, we sought to determine whether or not use of this substantially affected trial findings.