Insurance plans have lists of medications that they will pay for based on cost and previous effective results. Drugs that are not covered are those where the cost is typically more substantial than an equivalently effective medication...often pushing the generic over the name brand but occasionally one brand over another..or those where the efficacy is in question or have not been on the market long enough to establish an effective track record. Often insurers will through the appeals process, permit to cover the non-formulary non-experimental medication where (and only where) all formulary options have shown to be ineffective.
Doctors have access to these lists and are supposed to use them in the process of prescribing medications that will be covered but sometimes get confused on which insurers list they're looking at or look at the wrong year or simply make a mistake. Typically for any condition, the doctor has 3-18 different medications to choose between provided there are that many options available. While it may seem like a PITA, it goes a long way to reining in the already high cost of medication; a medication that is substantially more expensive than its competitors but does not appear to be more effective will be dropped from formulary...this pretty much insures that the medication will see a substantial sales drop until it corrects its cost to be in line to the market or develops a more effective version. Medications that have not been shown to be effective will be passed over for those that have.
This is actually precisely the sort of practice among insurers and care-providers that the ACA should encourage...it achieves cost-control and promotes effective outcomes without negatively affecting patient-care.
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