42 CFR § 410.29 - Limitations on drugs and biologicals.
Medicare part B does not pay for the following:
(a) Except as provided in § 410.28(a) for outpatient diagnostic services and § 410.63(b) for blood clotting factors, and except for EPO, any drug or biological which is usually self-administered by the patient.
(b) Any drug product that meets all of the following conditions:
(1) The drug product was approved by the Food and Drug Administration (FDA) before October 10, 1962.
(2) The drug product is available only through prescription.
(3) The drug product is the subject of a notice of opportunity for hearing issued under section 505(e) of the Federal Food, Drug, and Cosmetic Act and published in the Federal Register on a proposed order of FDA to withdraw its approval for the drug product because it has determined that the product is less than effective for all its labeled indications.
(4) The drug product is presently not subject to a determination by FDA, made under its efficacy review program, that there is a compelling justification of the drug product's medical need. (21 CFR 310.6 contains an explanation of the efficacy review program.)