The study was an open label, parallel group randomised trial (ISRCTN: 14352545) conducted in primary care. Adult smokers (n=633) were prescribed NRT patch, randomised to a top-up dose of NRT based explicitly either on OPRM1 genotype or heaviness of smoking and followed for 6-months. Outcomes measures were: proportion of prescribed NRT consumed in the first 28 days; and motivation to make another quit attempt among those not abstinent at 6-month follow-up.