route of administration oral route of administration http://purl.bioontology.org/ontology/MESH/D000284 http://purl.obolibrary.org/obo/NCIT_C38288 https://www.wikidata.org/wiki/Q285166 The introduction of a substance to the mouth or into the gastrointestinal tract by the way of the mouth, usually for systemic action. It is the most common, convenient, and usually the safest and least expensive route of drug administration, but it uses the most complicated pathway to the tissues and bioavailability varies. The disadvantages of method are hepatic first pass metabolism and enzymatic degradation of the drug within the gastrointestinal tract. This prohibits oral administration of certain classes of drugs especially peptides and proteins. oral administration