Interaction of certain macromolecules with the appropriate drug reduces the symptoms of the disease in humans. The activity of a drug is defined by its affinity and the binding specificity for the targeted molecule. Although these parameters could exhibit satisfactory values for some compounds, it doesn’t necessarily mean they are potential drugs. The drug characteristics associated with absorption, distribution, metabolism and secretion are described as ADME properties. Drugs can be found accidentally or designed according to structural information of the targeted molecule. The knowledge about the human genome, such as gene identification that could serve as a potential drug target, has a significant contribution to the new drug development. Final phases of the drug development including drug efficacy and side-effects testing are performed on the group of volunteers. Even when the drug is approved for the market use there is still a possibility that microorganisms and cancer cells gradually develop resistance to that drug, which is a major problem for humans.