When a pharmacy submits a claim for a compounded medication, they must provide the NDC of every ingredient in the compound. if one ingredient is not covered the insurance can either : 1. deny the entire compound claim or 2. reimburse for only the NDC covered at the 100% discounted pharmacy rate... (which is NOT what you pay at the retail pharmacy but what the insurance feels is reasonable and justified).
Most insurances will also make you pay for the compounded medication and submit for reimbursement.
If a medication requires a mixture, chances are they will make you go through a PBM, and will send you both the active and inactive ingredients with instructions on how to mix them.
Check with the PBM or insurance to see if it requires a prior authorization or a PLA.. Patient level authorization.. have to show all the other medications that are on the formulary or are covered does not work for you... standards PBM red tape.
You might have a closed formulary.. those are the worst.. only medications on the list are covered, nothing else is period.. no authorizations or recourse no matter what you and the dr say