When is the Medicare Advantage Disenrollment Period? January 1 through March 31. What can you do during this time? You can leave your current Medicare Advantage plan and switch to Original Medicare (Parts A and B) If you switch to Original Medicare, you can also join a Medicare prescription drug plan. Coverage begins the first day of the month after your enrollment form is received. What can’t you do during this time? You can’t switch from Original Medicare to a Medicare Advantage plan, or switch from one Medicare Advantage to another. You can’t switch from one Medicare prescription drug plan to another. You can’t join, switch, or drop a MSA (Medical Savings Account) Plan If you decide to switch back to Original Medicare (Parts A and B), you are eligible to apply for a Medicare Supplement plan. Visit our Medicare Supplement Plans page for more information.