A recent experiment by a team led by Niteesh Choudhry, a professor of medicine at Harvard, quantifies the problem. The experiment involved nearly 6,000 patients who had just suffered a heart attack, and were prescribed drugs known to reduce the chance of another one — statins, beta-blockers, angiotensin-converting-enzyme inhibitors or angiotensin-receptor blockers. Half had their co-pays for these drugs waived; the other half paid the usual fee.
As expected, more people in the zero co-pay group took the drugs, and their health improved. Those in the zero co-pay group were 31 percent less likely to have a stroke, 11 percent less likely to have another major “vascular episode” and 16 percent less likely to have a myocardial infarction or unstable angina. None of these benefits came at a net monetary cost. The insurers did not spend more in total. By some measures, they spent less.
Source: Sendhil Mullainathan in the NYT.