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Tricare is easy for us to work with.
Problem lies with some pharmacies. My wife was on narcotics for several years. We have a good quack. He prescribes the medicines for 90 day refills. In some cases, wife's dope was only 30 day supply with x number of refills.
We get our drugs through Walmart stores. When she needed refills, we located a pharmacy that was a couple to a few days out on our trips. We requested refill, Walmart if needed would electronically send refill request to quack. We never had any problems. We had one that the pharmacy didn't stock enough of the correct dose and had to wait for an extra day.
Do not bet on getting drugs at all military hospitals.