i think it makes no sense to have ambulatory plan within medical insurance. normally the insurance covers 80% of the cost of the medicine, up to a certain amount a year, from 3,000 to around 12,000. exact details will depend on the type of the plan. depending on the medicine 3,000 worth can be just one month supply.
in order to buy meds with insurance you also need a valid prescription so you need to visit a doctor, wasting time and spending money. there is a limit to how much medicine you can buy in one go and certain drugs can only be prescribed by a corresponding specialist. again, depends on the insurer and the plan. plus, of course, certain medicine are not covered at all. i've also seen requirement for pre-authorization.
it's probably best to keep ambulatory part of the plan to minimum to cover the costs of occasional treatments (infection, flue, whatnot) and buy daily medicine with cash. most pharmacies will offer a discount on purchases above certain value or quantity. or, if you are short on money you can buy most medicine per one pill to cover your daily needs.