How They're Used
Administration routes, bioavailability, and the reconstitution calculator
How Are Peptides Taken?
Most peptides can't survive your stomach acid, which is why injection is the most common route. But newer technologies are opening doors to oral, nasal, and topical delivery.
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Understanding Bioavailability
Bioavailability is the percentage of a drug that actually reaches your bloodstream. It's one of the most important concepts in peptide therapy -- and the reason most peptides need to be injected rather than swallowed.
What Destroys Peptides?
Three barriers work against oral peptides: stomach acid (pH 1-3) denatures the structure, digestive enzymes (pepsin, trypsin) cleave the peptide bonds, and the intestinal wall blocks large molecules from absorbing into blood.
The SNAC Breakthrough
Oral semaglutide (Rybelsus) uses SNAC (sodium N-[8-(2-hydroxybenzoyl)amino]caprylate) to temporarily raise stomach pH and enhance absorption. Even so, only ~1% of the dose reaches the bloodstream -- requiring a much higher oral dose than injectable.
Why Injection Works
Subcutaneous injection bypasses all three barriers. The peptide enters tissue directly, then slowly absorbs into the bloodstream through capillaries. This gives 50-80% bioavailability with predictable, consistent dosing.
The Future: Oral Peptides
Research is advancing rapidly on oral peptide delivery: enteric coatings, permeation enhancers, nanoparticle carriers, and micro-needle capsules (like Rani Therapeutics' RaniPill) may make needles obsolete within a decade.
The Reconstitution Lab
Injectable peptides come as a freeze-dried powder (lyophilized) that must be mixed with bacteriostatic water before use. This calculator helps determine the right concentration and syringe draw volume.
Storage & Handling
Peptides are delicate molecules. Improper storage is one of the most common reasons for reduced effectiveness. Understanding degradation pathways helps explain why strict handling protocols exist.
Common Questions About How Peptides Are Used
Short, sourced answers to the questions people ask most about how peptides are taken, why they're usually injected, and how to reconstitute and store them.
How are peptides administered?
Most peptides are administered by subcutaneous injection because they can't survive stomach acid, giving about 50-80% bioavailability and allowing self-administration. Other routes include oral (semaglutide with SNAC), nasal (Selank, Semax, oxytocin), topical (GHK-Cu creams), intravenous in clinical settings, and sublingual for some small peptides.
Why can't peptides be taken orally?
Three barriers destroy most oral peptides: stomach acid (pH 1-3) denatures their structure, digestive enzymes (pepsin, trypsin) cleave the peptide bonds, and the intestinal wall blocks large molecules from absorbing. Oral semaglutide (Rybelsus) is a rare exception using an absorption enhancer called SNAC, yet even then only about 1% of the dose reaches the bloodstream.
What is bioavailability in peptides?
Bioavailability is the percentage of a dose that actually reaches your bloodstream. It's a main reason most peptides are injected rather than swallowed: subcutaneous injection gives roughly 50-80% bioavailability and intravenous delivery about 100%, while oral peptides typically deliver under 1-2%.
How do you reconstitute a peptide?
Injectable peptides come as a freeze-dried (lyophilized) powder that must be mixed with bacteriostatic water before use. The amount of water sets the concentration -- for example, 5 mg in 2 mL gives 2.5 mg/mL -- which then determines the syringe draw volume. Gently swirl rather than shake the vial, since vigorous shaking can denature the peptide.
How should peptides be stored?
Lyophilized freeze-dried powder is the most stable form and can be kept at room temperature for weeks or refrigerated for months in a cool, dark, dry place. Once reconstituted, peptides must be refrigerated at 2-8C (36-46F) and are typically stable for 2-4 weeks. Never freeze reconstituted peptides, since ice crystals can denature the protein structure.
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Knowledge Check
Test what you learned in this module.
Practice Exercises
Reinforce your understanding with interactive exercises.