Abstract: We identified two new studies, giving a total of 10 studies, involving 3655 participants. The medication adherence interventions studied were all provided in addition to standard behavioural support.They typically provided further information on the rationale for, and emphasised the importance of, adherence to medication or supported the development of strategies to overcome problems with maintaining adherence (or both). Seven studies targeted adherence to NRT, two to bupropion and one to varenicline. Most studies were judged to be at high or unclear risk of bias, with four of these studies judged at high risk of attrition or detection bias. Only one study was judged to be at low risk of bias. Meta-analysis of all 10 included studies (12 comparisons) provided moderate-certainty evidence that adherence interventions led to small improvements in adherence (i.e. the mean amount of medication consumed; SMD 0.10, 95% CI 0.03 to 0.18; I² = 6%; n = 3655), limited by risk of bias. Subgroup analyses for the primary outcome identified no significant subgroup effects, with effect sizes for subgroups imprecisely estimated. However, there was a very weak indication that interventions focused on the 'practicalities' of adhering to treatment (i.e. capabilities, resources, levels of support or skills) may be effective (SMD 0.21, 95% CI 0.03 to 0.38; I² = 39%; n = 1752), whereas interventions focused on treatment 'perceptions' (i.e. beliefs, cognitions, concerns and preferences; SMD 0.10, 95% CI –0.03 to 0.24; I² = 0%; n = 839) or on both (SMD 0.04, 95% CI –0.08 to 0.16; I² = 0%; n = 1064), may not be effective. Participant-centred interventions may be effective (SMD 0.12, 95% CI 0.02 to 0.23; I² = 20%; n = 2791), whereas those that are clinician-centred may not (SMD 0.09, 95% CI –0.05 to 0.23; I² = 0%; n = 864). Five studies assessed short-term smoking abstinence (five comparisons), while an overlapping set of five studies (seven comparisons) assessed long-term smoking abstinence of six months or more. Meta-analyses resulted in low-certainty evidence that adherence interventions may slightly increase short-term smoking cessation rates (RR 1.08, 95% CI 0.96 to 1.21; I² = 0%; n = 1795) and long-term smoking cessation rates (RR 1.16, 95% CI 0.96 to 1.40; I² = 48%; n = 3593). In both cases, the evidence was limited by risk of bias and imprecision, with CIs encompassing minimal harm as well as moderate benefit, and a high likelihood that further evidence will change the estimate of the effect. There was no evidence that interventions to increase adherence to medication led to any adverse events. Studies did not report on factors plausibly associated with increases in adherence, such as self-efficacy, understanding of and attitudes toward treatment, and motivation and intentions to quit. In people who are stopping smoking and receiving behavioural support, there is moderate-certainty evidence that enhanced behavioural support focusing on adherence to smoking cessation medications can modestly improve adherence. There is only low-certainty evidence that this may slightly improve the likelihood of cessation in the shorter or longer-term. Interventions to increase adherence can aim to address the practicalities of taking medication, change perceptions about medication, such as reasons to take it or concerns about doing so, or both. However, there is currently insufficient evidence to confirm which approach is more effective. There is no evidence on whether such interventions are effective for people who are stopping smoking without standard behavioural support.

Plain-language summary: We searched for studies up to September 2018, and we found 10 studies, including 3655 people. All of these people were smokers, over 18 years of age. Studies tested different ways of helping people use their stop-smoking medicines properly. Typically this meant providing additional information about the medicine or helping people to overcome problems they had with taking the medicine. One study delivered support by telephone, and the rest provided at least some face-to-face support. All included studies measured the amount that people used their medicines and all but one measured how many people quit smoking. People who received help to improve their use of medicines to stop smoking used their medicines slightly more than people who did not receive this help. There was some evidence that this also led to slightly more people quitting smoking. The evidence that helping people improve their use of stop-smoking medicines can successfully boost the use of these medicines is of moderate quality, meaning that more evidence could make us feel more certain of this effect. This is because there were problems with the methods of some of the included studies. The evidence suggesting that approaches to improve the use of stop-smoking medicines can help more people to quit smoking is of low quality, which means that we are not confident that they do actually help more people to quit and further evidence may or may not strengthen our confidence in this effect. This is because there were problems with some of the study methods and because it is unclear whether providing extra support to encourage people to use their medicines leads to more or fewer people successfully quitting smoking.