| Summary: | Background A cointervention in a randomized clinical trial (RCT) is medical care given in addition to the tested intervention. If cointerventions are unbalanced between trial arms, the results may be biased. We hypothesized that cointerventions would be more adequately reported in RCTs without full blinding or at risk of bias. Methods and Results To describe the reporting of cointerventions and to evaluate the factors associated with their reporting, we did a systematic search of all RCTs evaluating pharmacological interventions on cardiovascular outcomes published in 5 high‐impact journals. The reporting of cointerventions, blinding, and risk of bias were extracted and evaluated independently by 2 reviewers (E.M., L.A.). Cointerventions were inadequately reported in 87 of 123 RCTs (70.7%), with 56 (45.5%) providing no information on cointerventions and 31 (25.2%) providing only partial information. Of the RCTs, 52 (42.3%) had inadequate blinding of participants and/or personnel and 63 (51.2%) of the RCTs were judged at risk of bias. In univariable analysis, the reporting of cointerventions was not associated with blinding of participants and/or personnel (odds ratio [OR], 1.04; 95% CI, 0.47–2.27 for adequately versus inadequately blinded trials) or with risk of bias (OR, 1.47; 95% CI, 0.67–3.21 for at low risk of bias versus trials at risk of bias). In multivariable analysis, only a follow‐up of <1 month was associated with the adequate reporting of cointerventions (OR, 3.63; 95% CI, 1.21–10.91). Conclusions More than two‐thirds of recent major cardiovascular trials did not adequately report cointerventions. The quality of reporting was not better among trials that were not fully blinded or at risk for bias. Registration URL: https://www.crd.york.ac.uk/PROSPERO/. Unique identifier: CRD42018106771.
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