Copayments cause many elderly Americans to put off filling prescriptions until their Social Security checks arrive. That’s the central finding of research Timothy J. LaytonDaniel Prinz, and I recently conducted. Even a copay of as little as five dollars can lead some people to delay acquiring important drugs such as antidepressants, insulin, statins, and blood thinners. With that in mind, insurers ought to structure the copayments that their beneficiaries face so that they do not cause delays in important care.