If you get VA health benefits and decide that VA drug coverage meets your needs, you should probably keep your coverage. An exception might be if you are eligible for Extra Help. You should contact your local VA facility before making any changes to your coverage.
VA coverage is considered creditable, or at least as good as Part D, so you will not have to pay a late enrollment penalty if you sign up within 63 days of involuntarily losing your VA coverage. If you don’t lose your coverage, and want to join a Medicare drug plan, you must wait for an annual enrollment period.