BACKGROUND: Older people taking multiple medications represent a large and growing proportion of the population. Managing multiple medications can be challenging, and this is especially the case for older people, who have higher rates of comorbidity and physical and cognitive impairment than younger adults. Good medication-taking ability and medication adherence are necessary to ensure safe and effective use of medications. OBJECTIVES: To evaluate the effectiveness of interventions designed to improve medication-taking ability and/or medication adherence in older community-dwelling adults prescribed multiple long-term medications. SEARCH METHODS: We searched MEDLINE, Embase, Cochrane Central Register of Controlled Trials (CENTRAL), PsycINFO, CINAHL Plus, and International Pharmaceutical Abstracts from inception until June 2019. We also searched grey literature, online trial registries, and reference lists of included studies. SELECTION CRITERIA: We included randomised controlled trials (RCTs), quasi-RCTs, and cluster-RCTs. Eligible studies tested interventions aimed at improving medication-taking ability and/or medication adherence among people aged ≥ 65 years (or of mean/median age > 65 years), living in the community or being discharged from hospital back into the community, and taking four or more regular prescription medications (or with group mean/median of more than four medications). Interventions targeting carers of older people who met these criteria were also included. DATA COLLECTION AND ANALYSIS: Two review authors independently reviewed abstracts and full texts of eligible studies, extracted data, and assessed risk of bias of included studies. We conducted meta-analyses when possible and used a random-effects model to yield summary estimates of effect, risk ratios (RRs) for dichotomous outcomes, and mean differences (MDs) or standardised mean differences (SMDs) for continuous outcomes, along with 95% confidence intervals (CIs). Narrative synthesis was performed when meta-analysis was not possible. We assessed overall certainty of evidence for each outcome using Grades of Recommendation, Assessment, Development and Evaluation (GRADE). Primary outcomes were medication-taking ability and medication adherence. Secondary outcomes included health-related quality of life (HRQoL), emergency department (ED)/hospital admissions, and mortality. MAIN RESULTS: We identified 50 studies (14,269 participants) comprising 40 RCTs, six cluster-RCTs, and four quasi-RCTs. All included studies evaluated interventions versus usual care; six studies also reported a comparison between two interventions as part of a three-arm RCT design. Interventions were grouped on the basis of their educational and/or behavioural components: 14 involved educational components only, 7 used behavioural strategies only, and 29 provided mixed educational and behavioural interventions. Overall, our confidence in results regarding the effectiveness of interventions was low to very low due to a high degree of heterogeneity of included studies and high or unclear risk of bias across multiple domains in most studies. Five studies evaluated interventions for improving medication-taking ability, and 48 evaluated interventions for improving medication adherence (three studies evaluated both outcomes). No studies involved educational or behavioural interventions alone for improving medication-taking ability. Low-quality evidence from five studies, each using a different measure of medication-taking ability, meant that we were unable to determine the effects of mixed interventions on medication-taking ability. Low-quality evidence suggests that behavioural only interventions (RR 1.22, 95% CI 1.07 to 1.38; 4 studies) and mixed interventions (RR 1.22, 95% CI 1.08 to 1.37; 12 studies) may increase the proportions of people who are adherent compared with usual care. We could not include in the meta-analysis results from two studies involving mixed interventions: one had a positive effect on adherence, and the other had little or no effect. Very low-quality evidence means that we are uncertain of the effects of educational only interventions (5 studies) on the proportions of people who are adherent. Low-quality evidence suggests that educational only interventions (SMD 0.16, 95% CI -0.12 to 0.43; 5 studies) and mixed interventions (SMD 0.47, 95% CI -0.08 to 1.02; 7 studies) may have little or no impact on medication adherence assessed through continuous measures of adherence. We excluded 10 studies (4 educational only and 6 mixed interventions) from the meta-analysis including four studies with unclear or no available results. Very low-quality evidence means that we are uncertain of the effects of behavioural only interventions (3 studies) on medication adherence when assessed through continuous outcomes. Low-quality evidence suggests that mixed interventions may reduce the number of ED/hospital admissions (RR 0.67, 95% CI 0.50 to 0.90; 11 studies) compared with usual care, although results from six further studies that we were unable to include in meta-analyses indicate that the intervention may have a smaller, or even no, effect on these outcomes. Similarly, low-quality evidence suggests that mixed interventions may lead to little or no change in HRQoL (7 studies), and very low-quality evidence means that we are uncertain of the effects on mortality (RR 0.93, 95% CI 0.67 to 1.30; 7 studies). Moderate-quality evidence shows that educational interventions alone probably have little or no effect on HRQoL (6 studies) or on ED/hospital admissions (4 studies) when compared with usual care. Very low-quality evidence means that we are uncertain of the effects of behavioural interventions on HRQoL (1 study) or on ED/hospital admissions (2 studies). We identified no studies evaluating effects of educational or behavioural interventions alone on mortality. Six studies reported a comparison between two interventions; however due to the limited number of studies assessing the same types of interventions and comparisons, we are unable to draw firm conclusions for any outcomes. AUTHORS' CONCLUSIONS: Behavioural only or mixed educational and behavioural interventions may improve the proportion of people who satisfactorily adhere to their prescribed medications, but we are uncertain of the effects of educational only interventions. No type of intervention was found to improve adherence when it was measured as a continuous variable, with educational only and mixed interventions having little or no impact and evidence of insufficient quality to determine the effects of behavioural only interventions. We were unable to determine the impact of interventions on medication-taking ability. The quality of evidence for these findings is low due to heterogeneity and methodological limitations of studies included in the review. Further well-designed RCTs are needed to investigate the effects of interventions for improving medication-taking ability and medication adherence in older adults prescribed multiple medications.