Most people have to enroll if they want prescription drug coverage, but the Part D benefit is completely voluntary. There is an exception, however, for certain very low- income seniors who receive Medicaid benefits: they are automatically enrolled in a Medicare prescription drug program. These low-income seniors are given the option to optout of Part D, but are not allowed to return to Medicaid for their prescription drug needs. In most cases, seniors who delay enrollment will be subject to penalties when they do sign up. The penalties do not apply if you have other drug coverage that is at least as good as Medicare’s.