Because oral administration is usually the safest, most convenient, and least expensive method, most drugs are administered by this route. Drugs for oral administration are available in many forms: tablets, enteric-coated tablets, capsules, syrups, elixirs, oils, liquids, suspensions, powders, and granules. Some require special preparation before administration, such as mixing with juice to make them more palatable; oils, powders, and granules most often require such preparation.

Sometimes oral drugs are prescribed in higher dosages than their parenteral equivalents because after absorption through the GI system, they are immediately broken down by the liver before they reach the systemic circulation.

Oral administration is contraindicated for unconscious patients; it may also be contraindicated in patients with nausea and vomiting and in those unable to swallow.