Do all peptides have to be injected?
Updated: 2026-09-09 · Basics
Short answer
Not all, but most. The obstacle is digestion: a swallowed peptide is usually broken down before it reaches the bloodstream. That is why injectable versions dominate, with some specially formulated oral, nasal or topical options. The route changes how much actually reaches the tissue, so routes are not interchangeable.
In plain English
- Subcutaneous injection: the most common route for systemic peptides.
- Oral: only viable with formulations designed to survive the stomach.
- Topical: useful when the target is the skin itself, as with GHK-Cu in skincare.
- Nasal: used for a few specific peptides.
What we know
- Gastrointestinal degradation limits oral bioavailability for most peptides.
- Some oral peptide drugs are approved thanks to specific formulation technology.
What we don't know yet
- For many over-the-counter products there is no proof the chosen route reaches useful tissue levels.