How Do Medicare Prescription Plans Work and what is the cost

You are eligible to enroll in a Medicare prescription plan as soon as you are entitled to Medicare Benefits. There are two types of private plans you can get benefits through, A Prescription Drug Plan (PDP) that provides Drug coverage only, or a Medicare Advantage plan with prescription drug coverage (MA-PD) also called Medicare Part C. some companies like AARP, Aetna, Cigna, and Humana offer $0 deductibles and offer immediate coverage. 
Medications can have a copay or coinsurance, but not both. Make sure you check with your Insurance agent and see if your medications are covered under the Plan.