yes. you can switch plans during medicare's annual enrollment period which runs from october 15th through december 7th each year. pre-existing medical conditions do not factor into your eligibility. the only exception to that is if you have original medicare and a medigap plan to help pick up costs medicare alone does not cover. after an initial enrollment period if you apply for a new medigap plan insurers can take the state of your health into consideration when deciding whether to sell you a plan and how much to charge. but if you have medicare advantage or want to switch your prescription drug plan (medicare part d) you can do that with no concern about pre-existing conditions as long as you do so during the open enrollment period.
can a person change medicare plans having preexisting conditions?