Most peptides are injected subcutaneously (under the skin, into fat tissue). A smaller number are injected intramuscularly (into muscle). The route affects absorption speed, injection technique, and needle selection.
Subcutaneous (SubQ) Injection
Subcutaneous injection delivers the peptide into the fat layer between the skin and the muscle. Absorption is slower and more gradual than intramuscular, which is desirable for most peptide protocols.
Technique:
- Clean the injection site with an alcohol swab. Let it dry.
- Pinch a fold of skin and fat between your thumb and index finger.
- Insert the needle at a 45-degree angle (for 1/2 inch needles) or 90 degrees (for 5/16 inch needles).
- Release the skin pinch.
- Push the plunger slowly and steadily.
- Wait 5-10 seconds before withdrawing the needle.
- Do not rub the site afterward. Light pressure with a cotton ball or swab is fine if there is a drop of blood.
Common SubQ Sites
Abdomen. The most popular site. Use the area around the belly button, staying at least 2 inches (5cm) away from the navel itself. Avoid the belt line. The abdomen offers a large, accessible surface area with consistent fat depth. Most peptide users start here.
Thigh (anterior/outer). Use the front or outer portion of the mid-thigh. Avoid the inner thigh (more nerve endings, more discomfort). The thigh provides good surface area for rotation but can be slightly more sensitive than the abdomen.
Upper arm (posterior). The back of the upper arm, between the shoulder and elbow. This site works well but is harder to reach without help. The fat layer here tends to be thinner, so use a shorter needle (5/16 inch) or a shallow angle.
SubQ Peptides
The following peptides are administered subcutaneously:
- BPC-157 - 2x daily
- Semaglutide - 1x weekly
- Tirzepatide - 1x weekly
- TB-500 - 2x weekly
- CJC-1295/Ipamorelin - 1x daily
- Sermorelin - 1x daily
- AOD-9604 - 1x daily
- PT-141 - as needed
- GHK-Cu - 1x daily
- DSIP - 1x daily
- MOTS-c - 3-5x weekly
Intramuscular (IM) Injection
Intramuscular injection places the peptide directly into muscle tissue. Absorption is faster due to higher blood flow in muscle. IM injections require longer needles (typically 1 inch or longer, 25g-27g) and a 90-degree angle.
Technique:
- Clean the site with an alcohol swab. Let it dry.
- Stretch the skin taut with one hand (do not pinch for IM).
- Insert the needle at 90 degrees in a quick, dart-like motion.
- Aspirate briefly (pull back on the plunger slightly). If blood appears, withdraw and try a new spot. Note: aspiration is no longer routinely recommended by most clinical guidelines, but some practitioners still advise it for IM injections.
- Inject slowly.
- Withdraw the needle and apply light pressure.
Common IM Sites
Deltoid (upper arm). The fleshy part of the outer shoulder. Good for small volumes (under 1ml). Easy to access.
Vastus lateralis (outer thigh). The outer middle third of the thigh. Accommodates larger volumes. Easy to self-administer.
Ventrogluteal (hip). The side of the hip. Preferred by many clinicians for its large muscle mass and low nerve density. Harder to self-administer without practice.
IM Peptides
Few peptides require intramuscular injection. Some can be given via either route:
If a peptide's administration route is listed as "subcutaneous," stick with SubQ. Do not switch to IM without reason.
Injection Site Rotation
Rotate your injection sites to prevent tissue problems. Repeatedly injecting in the exact same spot can cause:
- Lipodystrophy - hardened lumps or pitted areas in the fat tissue
- Scar tissue buildup - reduces absorption over time
- Localized pain or irritation - the tissue does not get time to recover
Rotation strategy:
For abdominal injections, picture a clock face around your navel. Each injection moves to the next "hour" position. This gives you 12 distinct spots on the abdomen alone. Add thigh and arm sites and you have weeks of rotation before returning to the same spot.
A simple rule: never inject within 1 inch (2.5cm) of your last injection site. Keep a mental pattern or, if you are prone to forgetting, alternate sides (left/right) on each injection day.
For daily peptides (like BPC-157 dosed 2x daily), a wider rotation pattern matters more. Consider using the abdomen for morning doses and the thigh for evening doses.
For weekly peptides (like semaglutide), rotation is simpler. Alternate between left and right abdomen, or switch between abdomen and thigh each week.
Consistent site rotation is one of the easiest ways to maintain injection comfort and absorption reliability over long protocols.