Introduction Smoke-free legislation has been instrumental in reducing secondhand smoke (SHS) exposure in public places. However, the evidence of the impact of institutional smoke-free policies in settings such as healthcare and defence is weaker. Specifically, the literature on the effect of smoke-free policies in military settings has not yet been synthesised.

Methods This review aimed to identify, critically appraise and synthesise the available evidence to evaluate the effect of defence smoke-free policies on SHS exposure. Eight electronic databases (eg, EMBASE, MEDLINE) were searched from inception to June 2020. We included English-language studies on smoke-free policies introduced in a defence setting, assessing their impact on SHS exposure (primary outcome) and healthcare utilisation, smoking behaviours and defence efficiency (secondary outcomes). Risk of bias was assessed using ROBINS-I. Synthesis without meta-analysis was conducted using vote counting of direction of effect.

Results The search retrieved 4503 citations of which eight met inclusion criteria; two controlled and six uncontrolled before-and-after studies. The evidence, although low-quality, from one study indicated reduced SHS exposure following the introduction of a defence smoke-free policy. For secondary outcomes the review found mixed results, with the quit rate being the one outcome favouring smoke-free policies. The cumulative confidence of evidence is uncertain and therefore reliable conclusions cannot be drawn from these studies.

Conclusions A research gap exists for high-quality studies on the impact of defence smoke-free policies which should use comparators and, if possible, randomisation. Policy-makers should introduce institutional smoke-free policies in defence settings within an evaluative framework to generate such evidence.