Pills that are chewed begin the digestion and absorption process in the mouth or stomach. Sometimes a drug is given orally at specific intervals to vary concentrations of the drug and balance desired effects with side effects. Injection is used when a medication would be inactive if digested, if a carefully controlled dose is needed, or if an immediate response is critical. Many vaccines are one-time injections into a muscle. Many injected medications are administered through an intravenous line directly into the bloodstream for faster and more predictable dosing.
Skin is another route of administration.
Creams, salves, ointments, and gels long have been used to treat skin problems, but now dermal patches can be used for medication that must be absorbed throughout the body. Though patches are becoming increasingly popular for other drugs as well, it can take several days for medication administered by patch to reach a therapeutic blood level, and the exact blood level can be difficult to control. Patches also tend to be an expensive way to administer a drug. Asthma patients often use steroid inhalers. Inhaled drugs tend to affect only the respiratory tract, resulting in fewer side effects.