The fraction of a dose that actually reaches your bloodstream in active form — the rest is lost to degradation or incomplete absorption.IV administration gives 100% bioavailability by definition. Subcutaneous injection typically gives 70–95% for peptides. Oral bioavailability of most peptides is near zero — peptidases in the GI tract degrade the peptide bond before it can be absorbed, and the GI epithelium is poorly permeable to large polar molecules. This is why nearly all research peptides require injection. Oral "peptide" products that claim equivalent bioavailability to injectable forms are making a claim that requires extraordinary evidence.