Peptide bioavailability

The fraction of an administered peptide that reaches systemic circulation in active form — typically very low orally because peptides are degraded by digestive enzymes.

Why it matters

Oral bioavailability of most peptides is in the 1–10% range or lower because gastric acid and intestinal proteases break peptide bonds before absorption. Injectable routes (subcutaneous, intramuscular) bypass GI degradation and deliver 70–100% bioavailability. Intranasal administration achieves intermediate bioavailability with much less invasive delivery.

In practice

For consumers the practical takeaway is that oral peptide supplements (collagen peptides notwithstanding, which are absorbed as amino acids rather than intact peptides) deliver far less active compound than injection. Marketing material that elides this delivers cost without effect.

Common confusion

“Oral peptides” is misleading if the product is actually delivering amino acids — the pharmacology is different.

This glossary entry is editorial content reviewed against primary sources. It is not medical advice. See our Editorial Policy.