Abstract: We included 65 randomised controlled trials from 12 countries involving patients undergoing a variety of procedures in hospitals. Nine thousand and twenty one patients were randomised and entered into these studies. Interventions used various designs and formats but the main data for results were from studies using written materials, audio-visual materials and decision aids. Some interventions were delivered before admission to hospital for the procedure while others were delivered on admission. Only one study attempted to measure the primary outcome, which was informed consent as a unified concept, but this study was at high risk of bias.  More commonly, studies measured secondary outcomes which were individual components of informed consent such as knowledge, anxiety, and satisfaction with the consent process.  Important but less commonly-measured outcomes were deliberation, decisional conflict, uptake of procedures and length of consultation. Meta-analyses showed statistically-significant improvements in knowledge when measured immediately after interventions (SMD 0.53 (95% CI 0.37 to 0.69) I2 73%), shortly afterwards (between 24 hours and 14 days) (SMD 0.68 (95% CI 0.42 to 0.93) I2 85%) and at a later date (15 days or more) (SMD 0.78 (95% CI 0.50 to 1.06) I2 82%). Satisfaction with decision making was also increased (SMD 2.25 (95% CI 1.36 to 3.15) I2 99%) and decisional conflict was reduced (SMD -1.80 (95% CI -3.46 to -0.14) I2 99%). No statistically-significant differences were found for generalised anxiety (SMD -0.11 (95% CI -0.35 to 0.13) I2 82%), anxiety with the consent process (SMD 0.01 (95% CI -0.21 to 0.23) I2 70%) and satisfaction with the consent process (SMD 0.12 (95% CI -0.09 to 0.32) I2 76%). Consultation length was increased in those studies with continuous data (mean increase 1.66 minutes (95% CI 0.82 to 2.50) I2 0%) and in the one study with non-parametric data (control 8.0 minutes versus intervention 11.9 minutes, interquartile range (IQR) of 4 to 11.9 and 7.2 to 15.0 respectively). There were limited data for other outcomes. In general, sensitivity analyses removing studies at high risk of bias made little difference to the overall results. Informed consent is an important ethical and practical part of patient care.  We have identified efforts by researchers to investigate interventions which seek to improve information delivery and consideration of information to enhance informed consent.  The interventions used consistently improve patient knowledge, an important prerequisite for informed consent.  This is encouraging and these measures could be widely employed although we are not able to say with confidence which types of interventions are preferable. Our results should be interpreted with caution due to the high levels of heterogeneity associated with many of the main analyses although we believe there is broad evidence of beneficial outcomes for patients with the pragmatic application of interventions. Only one study attempted to measure informed consent as a unified concept.

Plain-language summary: We searched the scientific literature to identify randomised controlled trials (RCTs) of interventions designed to improve informed consent in clinical practice.  We wanted to determine primarily whether these interventions improved all components of ‘informed consent’ (understanding, deliberation and communication of decision).  Other individual outcomes of direct relevance to patients (e.g. recall/knowledge, understanding, satisfaction and anxiety), those related to healthcare professionals (e.g. ease of use of intervention, satisfaction) and system outcomes (e.g. cost, rates of procedural uptake) were also assessed. We included 65 studies involving a total of 9021 patients.  The studies varied according to the type of intervention, the procedure for which consent was sought, the clinical setting and the outcomes measured.  Most interventions were written or audio-visual.  Only one study assessed all the elements of informed consent, but the design was not robust; all other studies assessed only components of informed consent.  When the results of multiple studies were combined, we found that interventions improved knowledge of the planned procedure, immediately (up to 24 hours), in the short term (1 to 14 days) and the long term (more than 14 days).  Satisfaction with decision making was increased; decisional conflict was reduced; and consultation length may be increased. There were no differences between the intervention and control for the outcomes of generalised anxiety, and either anxiety or satisfaction associated with the consent process. Limitations of the review include difficulties combining the results of studies due to variation in the procedures undergone by patients, the interventions used and outcomes measured.  This means that we are uncertain as to which specific interventions are most effective but pragmatic steps to improve information delivery and consideration of the information are likely to benefit patients.