Oral Bioavailability
The fraction of an orally taken drug that survives digestion and reaches circulation — typically under 1% for peptides.
Definition
Oral bioavailability is particularly low for peptides because gastric acid, pepsin and pancreatic enzymes break them down before absorption, and intestinal epithelium allows only small fractions of the surviving molecule through. Enteric-coated capsules and lipid-encapsulation approaches can raise bioavailability for select peptides (oral BPC-157 capsules, Selank oral drops) but the general rule remains: injection delivers a measurable dose, oral is adjunctive.
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Bioavailability
The fraction of a dose that reaches circulation in active form — a key reason most peptides are injected subcutaneously rather than taken orally.
MechanismFirst-Pass Metabolism
The breakdown of an orally administered drug by the gut and liver before it reaches systemic circulation — the reason most peptides are injected.
Delivery & DosingSubcutaneous InjectionSQ Injection
Injection into the fatty layer just below the skin — the standard route for peptide dosing, self-administered with an insulin syringe.
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