Drug administration is the method by which a drug is introduced into the body. In some cases, the method of drug administration can solve many of the problems associated with pharmacokinetics. The oral route is the easiest and most popular method of drug administration as far as the patient is concerned. However, there are several problems associated with rectal administration, including membrane irritation. There are four methods by which drugs can be injected into the body – by intravenous, intramuscular, subcutaneous or intrathecal injection. Some drugs can be absorbed through the mucous membranes of the mouth or nose, thus avoiding the digestive and metabolic enzymes encountered during oral administration. Injection of a drug produces a much faster response than oral administration, as the drug reaches the blood supply more quickly. Drugs taken in solution are absorbed more quickly and a certain percentage may even be absorbed through the stomach wall.