How do you find out what pharmaceutical company Rite Aid gets their medicine from?

You could ask them which company they got them from. I believe most pharmacies shop around and will purchase their next shipment from whichever company is offering the best deal at the time.

also chances are the root supplier on the chain is the same anyway…almost all ibuprofen in the UK, supermarket or prescription is almost certainly produced in the same factory that does different runs thought the day.

same with everything from ready meals to car parts its all coming from the same mass producers, hence the lowest price.

If you are talking about prescription meds, the pharmacist can tell you. If you are talking about OTC meds, the container generally has a telephone number to call if you have problems. Start there.