The Delivery Problem
The gastrointestinal tract is designed to break down proteins — and peptides are proteins. Proteases (pepsin, trypsin, chymotrypsin) cleave peptide bonds within minutes of oral ingestion. For most peptides, oral bioavailability is less than 1%.
This is why the majority of peptides must be injected subcutaneously. But alternative delivery methods exist for specific peptides, each with different bioavailability tradeoffs.
Subcutaneous Injection: The Gold Standard
Bioavailability: 89-95% (semaglutide prescribing information). SubQ injection deposits the peptide into the adipose layer beneath the skin, where it is absorbed into the systemic circulation over 15-60 minutes.
Advantages: Highest and most predictable bioavailability, well-established dosing protocols, works for all peptides.
Disadvantages: Requires reconstitution, sterile technique, needles, and cold storage. Injection anxiety is a barrier for many patients.
Oral Delivery: The Exception
Oral semaglutide (Rybelsus) achieves approximately 1% bioavailability using SNAC (sodium N-[8-(2-hydroxybenzoyl)amino] caprylate) technology. SNAC temporarily increases gastric pH and promotes transcellular absorption. The 14mg oral dose delivers roughly equivalent systemic exposure to 1mg SubQ.
BPC-157 is a special case: animal studies show oral BPC-157 survives gastric acid and accumulates locally in GI tissue. This makes oral delivery potentially useful for GI-specific applications (IBD, gastric ulcers), but NOT for systemic effects like tendon repair.
Intranasal Delivery
Bioavailability: 10-30% depending on the peptide. Intranasal delivery partially bypasses the blood-brain barrier via olfactory and trigeminal neural pathways, making it the preferred route for brain-targeted peptides.
Best candidates: Selank, Semax, oxytocin — small peptides targeting CNS receptors. Use sterile saline (not BAC water) as the vehicle to avoid nasal mucosa irritation.
Limitation: shelf life is short (10-14 days refrigerated) and dosing precision is lower than injection.
Transdermal and Sublingual
Transdermal: Very limited peptide penetration through intact skin. DMSO-based carriers can improve penetration for small peptides (like Dihexa) but introduce their own safety concerns. Not suitable for most peptides.
Sublingual: Some small peptides achieve modest absorption (5-15%) through the sublingual mucosa, bypassing hepatic first-pass metabolism. BPC-157 sublingual tablets/troches are marketed but have limited bioavailability data.
Bottom line: for systemic effects, subcutaneous injection remains the most reliable delivery method. Alternative routes are viable only for specific peptides with established data for that route.
Medical Disclaimer: This article is for educational purposes only. Consult a healthcare provider for delivery method recommendations.