Depending on the drug and its desired effect, there are a variety of administration methods. Most drugs are administered orally-that is, through the mouth. Only drugs that will not be destroyed by the digestive processes of the stomach or intestines can be given orally. Drugs can also be administered by injection into a vein (intravenously), which assures quick distribution through the bloodstream and a rapid effect; under the skin (subcutaneously) into the tissues, which results in localized action at a particular site as with local anesthetics; or into a muscle (intramuscularly), which enables rapid absorption through the many blood vessels found in muscles. An intramuscular injection may also be given as a depot preparation, in which the drug is combined with other substances so that it is slowly released into the blood.
Inhaled drugs are designed to act in the nose or lungs. General anesthetics may be given through inhalation. Some drugs are administered through drug-filled patches that stick to the skin. The drug is slowly released from the patch and enters the body through the skin. Drugs may be administered topically-that is, applied directly to the skin; or rectally-absorbed through an enema (an injection of liquid into the rectum) or a rectal suppository (a pellet of medication that melts when inserted in the rectum).