The way in which a substance is introduced into the body, such as oral ingestion, intravenous (IV), subcutaneous, or intramuscular injection, inhalation, smoking, or absorption through skin or mucosal surface, such as the gums, rectum, or genitalia. The manner of administration has a critical effect on the speed and intensity of drug effects and, hence, on the degree of intoxication, nature of risk exposure and dependence liability. It can also have a major influence on the nature and severity of undesirable effects and consequences, including body organ damage (e.g. lungs, veins) and infection transmission (e.g. hepatitis, HIV).