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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.
Methods
Our secondary analysis included all 2591 randomised participants of the PORTSSS trial. PORTSSS was a randomised controlled trial (RCT) of an English, government-funded quitline, comparing two forms of behavioural support, with and without the offer of a free NRT voucher using a parallel-group, factorial 2x2 design. Non-trial support used by participants included 'over the counter' NRT (n=498; 19.2%), NRT from health professionals (479; 18.5%), bupropion (37; 1.4%), varenicline (165; 6.4%), NHS stop smoking service support (125; 4.8%), NHS one-to-one therapy (221; 8.5%) and a non-NHS quitline (40; 1.5%); any support (978; 37.7%). Binary variables were created for each support type with recipients coded as 1 and non-recipients as 0. We used the same multivariable regression model as in the original trial analysis with...