42 CFR 423.2310 - Condition for coverage of drugs under Part D.
(a) Covered Part D drug coverage requirement. Except as specified in paragraph (b) of this section, in order for coverage to be available under Medicare Part D for applicable drugs of a manufacturer, the manufacturer must do all of the following:
(1) Participate in the Discount Program.
(2) Have entered into and have in effect an agreement described in § 423.2315(b).
(3) Have entered into and have in effect, under terms and conditions specified by CMS, a contract with the TPA.
(b) Exception to covered drug coverage requirement. Paragraph (a) of this section does not apply to an applicable drug if CMS has made a determination that the availability of the applicable drug is essential to the health of beneficiaries enrolled in Medicare Part D.