Why are New Medical Drugs Tested?

To ensure that they work, and are safe, before they can be prescribed. They are tested for: 1) Safety - This is important as some drugs are toxic, and have other side effects that might be harmful to people 2) Effectiveness - This is also known as efficacy, and checks how well the drug cures the disease, or improves symptoms 3) Dosage - This varies, and has to be closely controlled, as too high a concentration might be toxic