Pharmacology is the branch of medicine concerned with the uses, effects and modes of action of drugs. It studies how different chemicals affect biological systems, and incorporates knowledge and skills from a number of basic science disciplines including physiology, biochemistry, and cellular and molecular biology. As more medicines become available, pharmacology has become more important in determining the potential interactions caused by patients taking multiple prescribed, over-the-counter and even homeopathic medications. Whether these chemical agents are natural or synthetic, they can have physiological and behavioral effects on those that take them. It should be mentioned that pharmacology is one of the focal points of modern science and research activities. It seems that in the modern, high developed world all drugs and medicine are already invented and produced, but the up-to date realities and scientific achievements cause improvements of existing medicaments and creation of new efficient pharmaceutical substances.