28 Tex. Admin. Code § 21.3023
If the issuer of a health benefit plan, its delegated entity, or their employees or agents refuses to provide coverage for a prescription drug that is not included in a drug formulary, and the enrollee's physician or other health care provider with prescriptive authority has determined the prescription drug is medically necessary to treat a condition covered by the enrollee's health benefit plan, the refusal to provide coverage for the prescription drug constitutes an adverse determination for the purpose of Insurance Code Chapter 4201 . An enrollee may appeal the adverse determination under Insurance Code Chapter 4201, Subchapters H and I , and the issuer of the health benefit plan, and its employees or agents, must review and resolve the appeal in accordance with those sections.
28 Tex. Admin. Code § 21.3023