Medical drugs need to be tested before they are used as they need to ensure that the drugs work and ensure that they are safe before they can be prescribed. There are three main stages in the development and testing of a new drug. During stage one the drugs are tested using computer models and human cells that have been created and grown in a labortory. Many substances fail this test because they damage the human cells or don’t work. If the substances pass the first stage of the test, they are then tested on animals. These tests have to be carried outin the uk but testing animals with tobacco or cosmetic substances is illegal. These tests are carried out by injecting the animal with the substance then monitoring them for a certain amount of time to see if there is any side affects. They test on animals because humans and animals share many illnesses such as the hardening of the arteries which happens in both humans and rabbits, this means that testing on animals would give us a good understanding on if the drugs have any side effects as the illnesses are the same. If the substances pass animal testing then they move onto the third and final stage of testing which is clinical testing. During this stage willing volunteers are tested on to check if they are safe. The substances are then tested on people with the illnesses to ensure that they are safe and that they work.