What is Bioavailability? (Peptide Glossary)

Bioavailability is the proportion of a compound that reaches systemic circulation in active form. For most peptides, oral bioavailability is near zero: stomach acid and digestive enzymes dismantle peptide chains before absorption. This single fact shapes the entire research peptide field - it is why injection (subcutaneous or intramuscular) is the standard research route, and why intranasal and transdermal formats attract research interest as alternatives.

There are notable exceptions that prove the rule. BPC-157 is unusually stable in gastric juice (it derives from a gastric protein), which is why oral and capsule formats are researched for it specifically. Small peptides like KPV show oral activity in research models. And pharmaceutical engineering has produced oral semaglutide (Rybelsus) via an absorption enhancer - a famous exception that required enormous formulation effort.

For researchers evaluating product formats: a vendor selling a wide range of oral peptide capsules is either working with the handful of orally-stable exceptions or selling products with questionable research utility. Format plausibility is a quiet but useful vendor quality signal.