AbstractBackground and aimsOffering financial incentives is effective for smoking cessation during pregnancy. We tested the effectiveness of financial incentives for maintaining postpartum cessation, comparing 12‐month and 3‐month incentives with each other and with usual care (UC).Design, setting and participantsThis study was a pragmatic, multi‐centre, three‐arm randomized controlled trial involving four English, National Health Service, stop smoking services. A total of 462 postpartum women (aged ≥ 16 years) took part, who stopped smoking during pregnancy with financial incentives, validated as abstinent from smoking at end of pregnancy or early postpartum.InterventionsInterventions comprised (i) UC; (ii) UC plus up to £60 of financial voucher incentives offered to participants and £60 offered to an optional significant‐other supporter, over 3 months postpartum, contingent upon validated abstinence (‘3‐month incentives’); or (iii) UC plus ‘3‐month incentives’ plus £180 of vouchers offered to participants over 9 months postpartum, contingent upon abstinence (‘12‐month incentives’).MeasurementsPrimary outcome: biochemically validated abstinence at 1 year postpartum. To adjust for testing all comparisons between groups with equal precision, P < 0.017 was necessary for significance. Secondary outcomes: self‐reported and validated abstinence at 3 months postpartum; self‐reported abstinence at 1 year postpartum.FindingsPrimary outcome ascertainment: abstinence was 39.6% (63/159) 12 months incentives, 21.4% (33/154) 3 months incentives and 28.2% (42/149) UC. Adjusted odds ratios [95% confidence interval (CI)] = 12‐month versus 3‐month incentives OR = 2.41 (95% CI = 1.46−3.96), P = 0.001; 12 months versus UC 1.67 (1.04−2.70), P = 0.035; 3 months versus UC 0.69 (0.41−1.17), P = 0.174. Bayes factors indicated that for 12‐month versus 3‐month incentives and 12 months versus UC there was good evidence for the alternative hypothesis, and for 3 months versus UC there was good evidence for the null hypothesis.ConclusionsThis randomized controlled trial provides weak evidence that up to £300 of voucher incentives over 12 months is effective for maintaining smoking abstinence postpartum compared with usual care. There was good evidence that 12‐month incentives are superior to those over only 3 months, for which there was no evidence of effectiveness relative to usual care.