Objectives To evaluate the efficacy of intensive smoking cessation interventions (ISCIs) directly compared with shorter interventions (SIs), measured as successful quitting. Method Medline, Embase, the Cochrane Library and CINAHL were searched on 15 October 2021. Peer-reviewed randomised controlled trials (RCTs) of adult, daily smokers undergoing an ISCI were included. No setting, time or language restrictions were imposed. Risk of bias and quality of evidence was assessed using the Cochrane tool and Grading of Recommendations, Assessment, Development and Evaluation, respectively. Meta-analyses were conducted using a random-effects model. Results 17 550 unique articles were identified and 17 RCTs evaluating 9812 smokers were included. 14 studies were conducted in Europe or the USA. The quality of the evidence was assessed as low or moderate. Continuous abstinence was significantly higher in ISCIs in the long term (risk ratio 2.60, 95% CI 1.71–3.97). Direction and magnitude were similar in the short term; however, they were not statistically significant (risk ratio 2.49, 95% CI: 0.94–6.56). When measured as point prevalence, successful quitting was still statistically significant in favour of ISCIs, but lower (long term: 1.64, 1.08–2.47; short term: 1.68, 1.10–2.56). Sensitivity analysis confirmed the robustness of the results. Conclusion ISCIs are highly effective compared to SIs. This important knowledge should be used to avoid additional morbidity and mortality caused by smoking.