If you have a prescription for a drug that isn't on your plan's formulary, you should ask your doctor if there is another drug you can take that is on your plan's formulary. If your doctor can't find another drug on the formulary
that meets your needs, you will need to ask your plan for an exception
Your doctor must provide
your plan with a written or oral statement indicating that the drug is medically necessary to treat your disease/condition and that no other drugs on the formulary would be as effective for you as the non-covered drug, would have adverse effects, or both. You or your doctor should ask your plan what specific information it needs in order to process the exception request.
(Source: U.S. Department of Health & Human Services)