Abstract: We identified one study (290 randomised participants) that investigated the effectiveness of decision aids compared to standard information in the informed consent process for clinical trials. This study reported two separate decision aid randomised controlled trials (RCTs). The decision aid trials were nested within two different parent trials focusing on breast cancer in postmenopausal women. One trial focused on informed consent for treatment in women who had previously had surgery for ductal carcinoma in situ (DCIS), the other on informed consent for prevention in women at high risk for breast cancer. Two different decision aids were used in these RCTs, and were compared with standard information. The pooled findings highlight the uncertainty surrounding most reported outcomes, including knowledge, decisional conflict, anxiety, trial participation and attrition. There was very low quality evidence that decision aids lower levels of decisional regret to a small degree (MD -5.53, 95% CI -10.29 to -0.76). No data were identified on several prespecified primary outcomes, including accurate risk perception, values-based decision, or whether potential participants recognised that a decision needed to be made, were able to identify features of options that matter most to individuals, or were involved in the decision. There was insufficient evidence to determine whether decision aids to support the informed consent process for clinical trials are more effective than standard information. Additional well designed, adequately powered clinical trials in more diverse clinical and social populations are needed to strengthen the results of this review. More generally, future research on which outcomes are most relevant for assessment in this context would be helpful.

Plain-language summary: We reviewed the evidence about the effect of specific tools, called decision aids, which aim to improve decision making in the informed consent process for people who are considering participating in a clinical trial. These tools were compared to the standard process used for informed consent in clinical trials. There is currently not enough evidence to draw conclusions about the effectiveness of decision aids in the informed consent process for clinical trials. In clinical trials, one healthcare treatment is compared to another treatment or to no treatment. Before potential participants sign a consent form where they agree to take part in a clinical trial they must be given information about what will be expected of them and what they can expect. Research has shown that this information is often not as good as it could be. For example, people often misunderstand the information they have been given. Decision aids, which are tools that assist people to think about what matters most to them, support decision making for treatment and screening. Presenting information about trial participation through decision aids might improve the informed consent process by improving participants' knowledge, certainty with the decision and enabling them to consider what matters most to them personally. We searched the literature for studies where potential trial participants were randomly allocated to receive decision aids, compared to no decision aids or to other types of information for informed consent. We found one study, which reported data from two separate decision aid trials, where people who were given a decision aid alongside standard information were compared to people who were given standard information alone. When data from these two trials were combined, the results were inconclusive and not able to show whether people given the decision aid had any more or less knowledge or uncertainty about their decision, or were more or less likely to participate in a trial, than the people who were only given standard information. However, people who used the decision aid may have felt less regret about their decision. Overall there was very low quality evidence to support these findings, which means that there may be uncertainty around the results, and therefore, further research is required.