BACKGROUND: Although previous reviews demonstrated effectiveness related to medication adherence interventions, they incorporated various digital platforms and other multiple delivery modes, which makes difficult to distinguish what aspects of the interventions led to effectiveness. PURPOSE: This review aimed to (i) estimate the efficacy of face-to-face medication adherence interventions on adherence outcomes, in adults with Long Term Health Conditions (LTHCs) and (ii) identify the Behaviour Change Techniques (BCTs) used in the interventions and examine their potential impact on efficacy. METHODS: Cochrane Controlled Register of Trials, Embase, MEDLINE (Ovid), PsycINFO, Web of Science, PubMed, and Scopus databases were searched. Randomized controlled trials were included if they described an intervention to improve medication adherence, delivered via face-to-face only, and included patients with LTHCs. Studies were excluded if they used additional delivery modes, involved family members or used a group format. In addition, use of BCTs was coded. RESULTS: 20 studies were included (n = 3667). Statistically significant pooled effects were found favoring the intervention than control, for the following MEMS (electronic monitoring) measures: percentage of prescribed doses taken on time over a period of 3 weeks to 2 months (MD 9.34, 95% CI 4.36-14.33, p = .0002; I2 =0%); percentage of prescribed doses taken for a period of 1 week to 2 months (MD 5.63, 95% CI 1.62-9.64, p = .006; I2 = 51%) and for 1 month (OR = 2.51, 95% CI 1.37-4.57, p = .003; I2 = 0%); percentage of days correct doses taken for 1 month to 14 weeks (MD 6.59, 95% CI 0.74-13.15, p = .03; I2 = 68%). Studies using the Morisky scale showed a significant between group difference for 1-3 months (MD 0.86, 95% CI 0.59-1.13, p < .00001; I2 = 0%). Overall, more BCTs were identified in intervention conditions than in comparison conditions (22 vs. 10). The impact of BCTs on intervention effectiveness could not be established as the analyses were underpowered. CONCLUSIONS: Face-to-face interventions increased adherence to medication among adult patients with LTHCs. Although we were able to identify BCTs among interventions, data were insufficient to determine the impact of particular BCTs on intervention effectiveness.