Whenever you have two groups like this, one labeled the treatment group and the other the control group, we have an experiment gong on.
The treatment group gets the actual medication that is being tested. The control group gets a fake medication, aka placebo. Usually a placebo is meant for humans because it's more of a psychological factor. With cats, it likely won't affect them. However, such practices of having two groups like this is standard no matter what group of subjects you're testing.
The idea is that if the treatment group has better results compared to the placebo group, then it's likely the medication works.
