Key messages:

• Some medicines and e‐cigarettes (handheld devices that work by heating liquid that usually contains nicotine and flavourings) can help people to quit smoking for six months or longer.
• E‐cigarettes, and the medicines cytisine (otherwise known as Tabex) and varenicline (otherwise known as Chantix and Champix), appear to help the most people to quit smoking, followed by using two types of nicotine replacement therapy at once (nicotine patch and another type, such as gum or lozenge).
• We need more evidence on possible long‐term harms of e‐cigarettes and medicines to help people quit smoking, but there were very low numbers of serious harms found.

Authors' conclusions:
The most effective interventions were nicotine e-cigarettes, varenicline and cytisine (all high certainty), as well as combination NRT (additive effect, certainty not rated). There was also high-certainty evidence for the effectiveness of nicotine patch, fast-acting NRT and bupropion. Less certain evidence of benefit was present for nortriptyline (moderate certainty), non-nicotine e-cigarettes and tapering of nicotine dose (both low certainty). There was moderate-certainty evidence that bupropion may slightly increase the frequency of serious adverse events (SAEs), although there was also the possibility of no increased risk. There was no clear evidence that any other tested interventions increased SAEs. Overall, SAE data were sparse with very low numbers of SAEs, and so further evidence may change our interpretation and certainty. Future studies should report SAEs to strengthen certainty in this outcome. More head-to-head comparisons of the most effective interventions are needed, as are tests of combinations of these. Future work should unify data from behavioural and pharmacological interventions to inform approaches to combined support for smoking cessation.