How are new drugs developed and tested?

When a substance that is found that could be potentially useful for treating a disease, it can be developed into a drug. The drug then needs to be tested to check for safety, efectiveness and dosage. The drugs must be safe to use on patients so that they dont have any harmful side effects. The effectiveness of the drug for treating the disease must also be tested to ensure it is improves symptoms. Lastly the correct and safe dosage must be found which gives the optimum results.
First the drugs must be tested on computer models and tissue cultures which have been grown in the lab. This way it can begin to determine the safety and to check that they work on real cells. Secondly, the drugs are tested on animals to see how they work with a whole organism. Lastly, the drugs go through human trials in which at first small doses are given to healthy patients to check the safety, and then they are given to patients with the disease to check their effect on the symptoms and to determine the correct dosage.