Subcutaneous vs intramuscular
Peptides can be delivered by two main routes: subcutaneous (subq or SC) into the fatty tissue just under the skin, or intramuscular (IM) directly into muscle. The choice is not a preference — it's determined by the peptide.
| Subcutaneous (subq) | Intramuscular (IM) | |
|---|---|---|
| Absorption | Slow, sustained (acts as a depot) | Fast, peakier |
| Needle | 29–31G, 5/16" (8 mm) | 22–25G, 1" (25 mm) |
| Angle | 45–90° (pinch skin) | 90° (stretch skin) |
| Pain | Minimal with a fine needle | Moderate |
| Used for | BPC-157, TB-500, Semaglutide, Tirzepatide, CJC-1295, Ipamorelin, most research peptides | hCG (some protocols), oil-based hormones, vaccines |
Default assumption: if you don't know whether a peptide is subq or IM, it's subq. All glossary pages in our peptide reference note the route where relevant.
The four main subq sites
1. Abdomen (most common)
The area around the navel has consistent subcutaneous fat, clear anatomy, and is the easiest site for self-injection. Stay at least 2 inches (5 cm) from the navel in all directions and avoid the waistband area where clothing friction irritates fresh sites.
Divide the abdomen into four quadrants around the navel: upper-left, upper-right, lower-left, lower-right. Each quadrant can be further split into 4 zones for a systematic 16-zone rotation.
2. Outer thigh
The front-outer (anterolateral) portion of each thigh has a clear band of subcutaneous fat. Mark an imaginary rectangle one handwidth below the hip and one handwidth above the knee, centered between the midline and the outer seam of a pant leg. Inject anywhere within that rectangle.
Thighs work well for people who are leaner (less abdominal fat) and for rotating away from the abdomen during high-frequency dosing.
3. Back of upper arm
The posterior upper arm — the "tricep fat pad" — is a valid subq site but hard to self-administer. If you can get a helper or have good flexibility, it's useful for rotation. Avoid the biceps area (less fat, more nerves).
4. Upper buttock / flank (love handle)
The upper outer quadrant of the buttock and the flank just above the iliac crest (hip bone) are roomy subq sites favoured by some users. Good for adding rotation depth when abdomen and thighs are getting heavy use.
Body map overview
Main subcutaneous sites: 4-quadrant abdomen (primary), outer thighs, posterior upper arms.
How to rotate properly
Two rules govern rotation:
- Minimum 2 cm (one fingerwidth) from any injection used in the last 72 hours.
- Wait at least 3–7 days before reusing the exact same spot.
Systematic quadrant rotation
For daily peptides (BPC-157, CJC-1295 + Ipamorelin, Sermorelin), divide each main area into 4 quadrants and rotate through them in order:
- Day 1 → Upper-left abdomen
- Day 2 → Upper-right abdomen
- Day 3 → Lower-left abdomen
- Day 4 → Lower-right abdomen
- Day 5 → Left thigh, outer
- Day 6 → Right thigh, outer
- Day 7 → Back to upper-left abdomen (different spot within the quadrant)
Within each quadrant, also vary the exact spot — don't hit the same square centimeter every time. A full rotation cycle across 6–8 sub-zones gives each spot 6–8 days to recover.
Weekly peptides
For once-weekly peptides like Semaglutide, Tirzepatide, and Retatrutide, rotation matters less per dose but still matters across months. Alternate sides of the abdomen weekly, and switch to thighs every 4–6 weeks for variety.
The Peptide Protocol app has a built-in site rotation feature with a body-map overview that shows which sites are "ready," "cooling down," or "recommended next" — you can see a screenshot of it on the homepage.
Injection technique (7 steps)
Assumes a subcutaneous injection with an insulin syringe. If you are using a larger gauge or intramuscular route, adjust needle angle and depth accordingly.
- Wash hands
Soap and water for 20 seconds. Dry thoroughly before handling anything sterile. - Draw the dose
Swab the vial top, invert, draw the calculated unit amount. Tap the syringe to move bubbles up and eject them before measuring the final volume. - Pick the site
Choose a spot at least 2 cm from any recent injection. Use your rotation schedule. - Clean the skin
Wipe with an alcohol swab in a single direction. Let air-dry for 10–15 seconds — wet alcohol stings when the needle enters. - Pinch and insert
Pinch a 2–3 cm fold of skin and subcutaneous fat. Insert the needle at 45° if you pinched a thin fold, 90° for a thicker one. Fast, confident entry is less painful than slow. - Inject slowly
Push the plunger over 3–5 seconds. Faster injections sting more and can cause leakage. Release the pinch once the plunger bottoms out, then count to 3 before withdrawing. - Withdraw and log
Pull out at the same angle. Apply gentle pressure with gauze if bleeding — do not rub. Drop the syringe into a sharps container. Log the site, dose, and time.
Avoiding lipohypertrophy and scar tissue
Lipohypertrophy is a thickened, fibrotic, rubbery lump that forms when the same site is injected repeatedly. It's the #1 chronic complication of injection-based protocols. Beyond being visibly unattractive, it causes two real problems:
- Unpredictable absorption. Scarred tissue has reduced blood supply — peptide absorbs slower and less completely. Your "dose" becomes effective dose minus variance.
- Long-term cosmetic damage. Lumps can persist for months to years after you stop hitting the site.
Prevention is rotation. Once lipohypertrophy forms, stop using the affected area for 2–3 months; gentle massage can help, but don't expect rapid resolution.
Signs you're over-using a site
- A visible or palpable firm lump under the skin
- Injection-site pain that persists more than a few hours
- Blood or clear fluid leaking after withdrawal
- Bruising that appears in the same spot repeatedly
Frequently asked
Where should I inject peptides?
Most peptides go subcutaneously into the abdomen, at least 2 inches from the navel. Outer thighs and posterior upper arms are the next most common sites.
How often should I rotate sites?
Every injection should be in a different spot. Divide each area into 4 quadrants and rotate daily; aim for 3–7 days before reusing the exact same spot.
Is subq or IM better for peptides?
Subq is almost always the correct route for research peptides — they're designed to absorb slowly from fat tissue. IM is for specific clinical peptides or oil-based hormones.
How deep should the needle go?
For subq with a 5/16" (8 mm) insulin-syringe needle: all the way in. The needle is designed for that depth. Pinch the skin if you have very little subcutaneous fat to avoid hitting muscle.
Does it matter which side of the body I inject?
Not pharmacologically — but rotating across sides (left abdomen day 1, right day 2) is how you build systematic rotation. Don't favor one side.
Is it normal to bleed a little after injection?
Small beads of blood or a tiny bruise are normal and mean you nicked a capillary. If you hit a small vein and get a larger bruise, apply pressure for a minute and pick a different spot next time.