The aim of this chapter is to focus on the nursing pharmacology. A drug or medication is any substance that modifies body physiology when consumed in the body. Therefore, pharmacology may be defined as the study of drugs. This includes their origin, chemical structure, preparation, administration, actions, metabolism and excretion. Medication or drug is a chemical substance used in diagnostic, therapeutic and preventive aspects of a disease. This chapter covers the drug legislation related to tobacco and drugs, use of drugs, types of drugs and their mode of action, drug administration, nursing responsibilities in drug administration, medication orders, safety factors in preventing medication errors, patients education and compliance to therapeutic regimen, dosage calculation, and system of measurement.