The answer to this question would be giving the drug to a patient with the disease.
Clinical trial for a new drug has a few phase. Before giving the drug to a patient, you need to find information about how the drug absorbed and removed. Then you must prove that the drug is safe. So, a few earlier phase is dedicated to finding the side effect of the drug.
If the drug safe, you need to compare it with present drug to find which was superior than other
