Administration routes explained

1. Why route matters

The route of administration determines how much of an active compound reaches systemic circulation (bioavailability), how quickly it peaks, and how long it acts. For peptides, this is especially important because most are rapidly broken down by digestive enzymes — meaning not all routes are equally effective for all compounds.

2. Subcutaneous (sub-Q)

Sub-Q is the default and most common route for research peptides. The needle enters the fatty tissue just below the skin (not into muscle), where the peptide is absorbed through capillaries into systemic circulation.

• Bioavailability: Effectively complete for most peptides — sub-Q bypasses first-pass digestive breakdown.
• Absorption profile: Slower, more sustained than IM — suited to most research peptide pharmacokinetics.
• Equipment: 28–31G insulin syringe, 6–8 mm needle.
• Sites: Abdomen, outer thigh, tricep fat.

See the injection technique guide for detailed sub-Q procedure.

3. Intramuscular (IM)

IM injections go directly into muscle tissue. Absorption is faster than sub-Q due to higher blood flow through muscle. IM is used for a small number of research peptides where faster onset is desired or where IM-specific pharmacokinetic data exists.

• Typical sites: Gluteus medius, vastus lateralis (outer thigh), or deltoid.
• Needle: 21–25G, 25–38 mm — longer and wider than insulin syringes.
• Volume: Maximum 2–3 mL per IM site for large muscles.

4. Intranasal

Intranasal delivery bypasses the blood-brain barrier for some peptides by using the olfactory nerve pathway — making it valuable for CNS-active compounds where direct brain delivery is the goal. It also avoids injections entirely.

• Best suited for: Semax, Selank, NA-Semax, NA-Selank, BPC-157 (for CNS injury), DSIP, Oxytocin, VIP
• Bioavailability: Variable — 5–40% depending on the peptide, nasal mucosa condition, and technique. Lower than injectable but convenient.
• Equipment: 1 mL nasal atomiser (MAD device) or commercial nasal spray.
• Concentration: Intranasal peptides are typically more concentrated than injectable formulations to compensate for lower bioavailability. Capital Peptides nasal products are formulated for direct nasal use.

5. Oral

Most peptides are rapidly digested by stomach acid and proteolytic enzymes, making oral delivery largely ineffective for systemic action. However, there are important exceptions:

• BPC-157 oral: Animal data suggests oral BPC-157 is effective for gastrointestinal-specific applications (gut inflammation, ulcers) even when systemic absorption is low — because the peptide acts locally along the GI tract.
• Very short peptides (di/tripeptides): Some survive digestion. The bioregulator peptides (Epithalon, Pinealon, etc.) are sometimes taken sublingually or orally in some protocols.
• Approved GLP-1 oral drugs: Semaglutide (Rybelsus) is an approved oral formulation using a specific absorption enhancer (SNAC) — this technology is not applicable to DIY oral reconstitution.

6. Which route for which peptide

Check the specific research overview for each peptide for route-specific dosing differences.