Non-invasive brain stimulation for smoking cessation: a systematic review and meta-analysis

Background and Aims Non-invasive brain stimulation (NIBS) methods have showed promising results for the treatment of tobacco use disorder, but little is known about the efficacy of NIBS on sustained tobacco abstinence. We aimed to assess its effectiveness for long-term smoking cessation. Methods Systematic review and meta-analysis of randomized controlled trials (RCT). PubMed, Cochrane library, Embase, PsycINFO and clinical trials registries were systematically searched for relevant studies up to May 2021. Relevant studies included adult smokers seeking smoking cessation, included in an RCT using NIBS [specifically repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS)], and with follow-up of more than 4 weeks. There were no restrictions on location. Abstinence rates in the active NIBS groups were compared with abstinence rates in sham NIBS or in usual treatment groups, from 4 weeks to 12 months following the quit attempt. Smoking abstinence was measured on an intention-to-treat basis and we used risk ratios (RRs) as measures of effect size. Results Seven studies were included (n = 699 patients). In all included studies, the control groups were receiving sham NIBS and only data from 3 to 6 months were analysable. By pooling the seven included studies, the RR of sustained abstinence of any form of NIBS relative to sham NIBS was 2.39 [95% confidence interval (CI) = 1.26-4.55; I-2 = 40%]. Subgroup analyses found that the RR was even higher when excitatory rTMS was used on the left dorsolateral prefrontal cortex (RR = 4.34; 95% CI = 1.69-11.18; I-2 = 0%) or when using deep rTMS targeting the lateral prefrontal cortex and insula bilaterally (RR = 4.64; 95% CI = 1.61-13.39; I-2 = 0%). A high risk of bias was found in four included studies. We also determined, using grades of recommendation, assessment, development and evaluation, that overall there was a low level of confidence in the results. Conclusion Non-invasive brain stimulation (NIBS) may improve smoking abstinence rates from 3 to 6 months after quitting smoking, compared with sham NIBS or usual treatment.