Plans use a wide range of restrictions to steer beneficiaries toward lower-cost drugs and lower utilization. For example, most plans arrange the drugs they cover in a “tiered” formulary. This means some drugs (typically generics) will cost the least, with preferred drugs costing somewhat more, and non-preferred drugs costing the most. If you need a drug on a high tier, you will pay more for it unless your doctor can show that you need the more expensive drug and the plan grants an exception to its formulary limits.
Another common restriction is “prior authorization,” where your prescription will not be covered unless you contact the plan for permission first. Very often, your doctor will also have to contact the plan to explain the medical reasons why you need a drug.
Also, plans often have “step therapy” requirements. Such a limit would require you to first try a less expensive drug in a category and show that it does not work before you can move to a more expensive drug. You may be able to secure an exception to the step requirement if your doctor can show you tried the similar and less expensive drug previously and it did not work.
Some plans may limit the number of pills you can buy at one time, and they may also encourage you to use mail order pharmacies.