You know how when you go to the doctor and they write you a prescription for medicine? Well, sometimes the people who pay for your health care (like your parents' insurance company or the government) make a list of all the different medicines they will pay for. This list is called a formulary.
The reason they make this list is because there are lots and lots of different medicines out there, and some are cheaper than others. So the people who pay for your health care want to make sure they are using their money wisely and only paying for medicines that work well and are not too expensive.
But sometimes, people don't agree on which medicines should be on the formulary list. For example, some people might think that a certain medicine works really well, but it's really expensive. Other people might say that they have tried that medicine and it didn't work for them, so they think it shouldn't be on the list.
This disagreement is what we call a "formulary controversy". It's just a fancy way of saying that people can't agree on which medicines should be paid for by insurance or government programs. Sometimes this controversy can be very complicated and involve lots of arguments and debates, but it's all about trying to make sure that people get the best health care possible while also using resources wisely.