The Insulin Resistance Intervention after Stroke (IRIS) trial is a randomized clinical trial that will test the effectiveness of a new approach to preventing stroke and heart attack among patients with a recent stroke or TIA. The new approach targets insulin resistance, a newly-recognized cause of atherosclerosis. Atherosclerosis is the underlying disease that clogs vessels in strokes and heart attacks. Insulin resistance affects nearly half of all patients with stroke and ischemic TIA.

Participating stroke patients will be assigned to receive pioglitazone, a medication which reduces insulin resistance, or placebo (an inactive look-alike pill). Patients will stay on their assigned treatment for about four years. At the end of the study, investigators will compare the experience of patients on pioglitazone and placebo to see which group had fewer recurrent strokes and heart attacks.