Some drugs used to treat noncardiovascular conditions may adversely impact the cardiovascular status of individuals both with and without known cardiovascular disease. When the US Food and Drug Administration judges the potential cardiovascular safety signal to be of sufficient concern, it may require the pharmaceutical manufacturer of the drug in question to conduct a postmarketing (phase 4) randomized controlled trial (RCT). Although historically many phase 4 RCTs focused on efficacy (using a superiority design), contemporary phase 4 RCTs often are focused on safety and use a noninferiority design. The choices made by investigators during the planning stage of a postmarketing phase 4 RCT dedicated to the evaluation of cardiovascular safety can influence the ability to compare the standard and test agents. Multiple factors reflecting the conduct of a phase 4 RCT for a general medical condition may influence interpretation of a cardiovascular safety signal. The higher the rates of failure to adhere to the protocol and dropout from the study, the greater the risk of bias. Trials evaluating the cardiovascular safety of nonsteroidal anti-inflammatory drugs (NSAIDs) when used for arthritis are difficult to conduct and even more challenging to interpret. Concerns include the comparison of drug regimens that do not provide comparable analgesic efficacy and problems with adherence to the protocol and retention in the study. On the basis of phase 4 RCTs of NSAIDs to date, it appears that a comparatively low dose of celecoxib administered to low-risk subjects is associated with approximately the same cardiovascular risk as NSAIDs with less cyclooxygenase-2 inhibitory activity, but at the cost of not controlling arthritic pain as effectively.