Consent in clinical trials: what do patients know?

To assess participants' knowledge of key aspects about the clinical trials in which they are enrolled, describe the consent process, and assess the importance that investigators give to various aspects of trial information when verbally informing candidates.

Prospective study based on a structured questionnaire interview of participants within 3 months after trial enrollment and an anonymous questionnaire sent to clinical trial investigators.

A total of 140 participants included in 40 clinical trials were interviewed, and 51 investigators answered the questionnaire.

The formal steps to obtain informed consent were usually carried out. Participants were aware of the purpose of the trial and the right to discontinue participation, but only 23% knew that treatment was randomly allocated, 57% knew they might receive a placebo, and 42% was aware that adverse effects could occur. Patients who had read the information sheet had better knowledge of most aspects, except for the risk of adverse effects. The investigators considered that compensation, insurance coverage, possibility of receiving a placebo, and treatment allocation were the least important aspects of the trial when informing candidates for participation.

Although the formal steps for obtaining informed consent were usually carried out, a relevant percentage of patients included in clinical trials were unaware of important aspects of their participation. Patients showed more limited knowledge about the same points that investigators considered less important when informing potential participants. Deferring signature on the consent form and encouraging reading of the information sheet may improve participants' knowledge about clinical trials.