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We use the design of Medicare’s prescription drug benefit program to demonstrate three facts about the health consequences of cost-sharing. First, we show that an as-if-random increase of 33.6% in out-of-pocket price (11.0 percentage points (p.p.) change in coinsurance, or $10.40 per drug) causes a 22.6% drop in total drug consumption ($61.20), and a 32.7% increase in monthly mortality (0.048 p.p.). Second, we trace this mortality effect to cutbacks in life-saving medicines like statins and antihypertensives, for which clinical trials show large mortality benefits. We find no indication that these reductions in demand affect only ‘low-value’ drugs; on the contrary, those at the highest risk of heart attack and stroke, who would benefit the most from statins and antihypertensives, cut back more on these drugs than lower risk patients. Similar patterns exist for other drug–disease pairs, and irrespective of socioeconomic circumstance. Finally, we document that when faced with complex, high-dimensional choice problems, patients respond in simple, perverse ways. Specifically, price increases cause 18.0% more patients (2.8 p.p.) to fill no drugs, regardless of how many drugs they had been on previously, or their health risks. This decision mechanically results in larger absolute reductions in utilization for those on many drugs. We conclude that cost-sharing schemes should be evaluated based on their overall impact on welfare, which can be very different from the price elasticity of demand.