(1) The provisions of these formulary rules apply to all claims arising on or after April 1, 2019, but only with respect to outpatient services.

(2) For claims arising before April 1, 2019, which are referred to as "legacy claims," the rules in this subchapter will apply to prescriptions written on or after April 1, 2020, or 90 days after the insurer gives notice as provided in ARM 24.29.1631, whichever is later.

(3) The provisions of this subchapter, including the formulary adopted and automatically updated as provided in ARM 24.29.1616 apply as they are in effect on the date the prescription is written.

(4) Nothing in this subchapter excuses an insurer from providing medications that constitute primary medical services required to be furnished by 39-71-704, MCA.

(5) Nothing in this subchapter requires an insurer to use the services of a PBM.