Pharmacology is the study of drugs. It involves examining the interactions of chemical substances with living systems, with a view to understanding the properties of drugs and their actions, including the interactions between drug molecules and drug receptors and how these interactions elicit an effect. Pharmacology comprises drug composition and properties, synthesis and drug design, molecular and cellular mechanisms, systems mechanisms, signal transduction, molecular diagnostics, interactions, toxicology, chemical biology, therapy, and medical applications and anti-pathogenic capabilities. The two main parts of pharmacology are pharmacodynamics and pharmacokinetics. Pharmacodynamics studies the effects of the drug on biological systems and the pharmacokinetics studies the effects of biological systems on the drug. pharmacodynamics describes the chemicals with biological receptors, and pharmacokinetics describes the absorption, distribution, metabolism, and excretion (ADME) of chemicals from the biological systems. Pharmacology also deals with the research, discovery and description of chemicals which show biological effects and the illumination of cellular and organismal function in relation to these chemicals. .