42 C.F.R. § 423.2708 – Conditions for coverage of drugs under Part D.

(a) General rule. Except as specified in paragraph (c) of this section, in order for coverage to be available under Part D for a Part D drug of a manufacturer that is an applicable drug or a selected drug during a price applicability period—
1. (1) The FDA-assigned labeler code of such applicable drug or selected drug must be covered by a Manufacturer Discount Program agreement (described at § 423.2752) that is in effect;
2. (2) The manufacturer must participate in the Manufacturer Discount Program in accordance with paragraph (b) of this section; and
3. (3) The manufacturer must have entered into and have in effect a Manufacturer Discount Program agreement in accordance with paragraph (b) of this section.
(b) Participation in the Manufacturer Discount Program. A manufacturer is considered to participate in the Manufacturer Discount Program and to have entered into and have in effect a Manufacturer Discount Program agreement for the purposes of paragraph (a) of this section if the manufacturer does either of the following:
1. (1) Executes and has in effect its own Manufacturer Discount Program agreement.
2. (2) Participates in the Manufacturer Discount Program by means of an arrangement whereby its labeler code(s) is covered by another manufacturer's Manufacturer Discount Program agreement that is in effect.
(c) Exception. Paragraph (a) of this section does not apply to an applicable drug that is not covered by a Manufacturer Discount Program agreement if CMS has made a determination that the availability of the drug is essential to the health of Part D enrollees. This exception to the general rule in paragraph (a) of this section does not apply to any applicable drug or selected drug of a manufacturer for any period described in section 5000D(c)(1) of the Internal Revenue Code of 1986 with respect to such manufacturer.
(d) Non-applicable drugs. Coverage under Part D is available for non-applicable drugs (as defined at § 423.100) of a manufacturer regardless of whether the manufacturer participates in the Manufacturer Discount Program or has a Manufacturer Discount Program agreement in effect.