Despite modern technologies, developing a new drug is still a costly and time-consuming process. Many potential pharmaceutical agents, which passed a number of extensive tests in the lab, fail during the clinical phase of testing. In the clinical phase, the agent is tested on healthy and later on sick people to determine possible side-effects of the treatment. When an agent has passed all kinds of different tests in the individual phases, it is able to become the active pharmaceutical ingredient of the new drug.
In order to save time and money, bioinformaticians try to simulate the molecules on a computer. In the early phase of drug development, the computer is used to filter out molecules that are predicted to bind not to the target molecule; this is done prior to expensive lab tests! After several molecules have been identified as potential agents, modifications of these molecules that, e.g., might allow a lower dosage or might weaken the side-effects are simulated on the computer before these optimizations of the agent are applied and tested in the real world.