A prescription drug plan is one option for individuals who want to enroll in the Medicare Part D prescription drug coverage, which subsidizes the costs of prescription drugs for enrollees. A prescription drug plan is a stand-alone plan, covering only prescription drugs. Enrollees who choose the option of prescription drug coverage through a Medicare Advantage plan would also have coverage for other medical expenses as part of that plan. Enrollees pay a co-pay for each prescription, a monthly premium and an annual deducible.