42 C.F.R. § 447.53 – Cost sharing for drugs.

(a) The agency may establish differential cost sharing for preferred and non-preferred drugs. The provisions in § 447.56(a) shall apply except as the agency exercises the option under paragraph (d) of this section. All drugs will be considered preferred drugs if so identified or if the agency does not differentiate between preferred and non-preferred drugs.

(b) At state option, cost sharing for drugs may be established at or below the amounts shown in the following table (except that the maximum allowable cost sharing shall be increased each year, beginning October 1, 2015, by the percentage increase in the medical care component of the CPI-U for the period of September to September of the preceding calendar year, rounded to the next higher 5-cent increment. Such increase shall not be applied to any cost sharing that is based on the amount the agency pays for the service):

Services	Maximum allowable cost sharing
Individuals with family income ≤150% of the FPL	Individuals with family income >150% of the FPL
Preferred Drugs	$4	$4.
Non-Preferred Drugs	8	20% of the cost the agency pays.

(c) In states that do not have fee-for-service payment rates, cost sharing for prescription drugs imposed on individuals at any income level may not exceed the maximum amount established for individuals with income at or below 150 percent of the FPL in paragraph (b) of this section.
(d) For individuals otherwise exempt from cost sharing under § 447.56(a), the agency may impose cost sharing for non-preferred drugs, not to exceed the maximum amount established in paragraph (b) of this section.
(e) In the case of a drug that is identified by the agency as a non-preferred drug within a therapeutically equivalent or therapeutically similar class of drugs, the agency must have a timely process in place so that cost sharing is limited to the amount imposed for a preferred drug if the individual's prescribing provider determines that a preferred drug for treatment of the same condition either will be less effective for the individual, will have adverse effects for the individual, or both. In such cases the agency must ensure that reimbursement to the pharmacy is based on the appropriate cost sharing amount.