Pinc PeptideThe girly peptide research blog

Guide · updated 8 October 2026

Peptide injection sites: what the approved labels say

Approved peptide injections such as Zepbound, Wegovy and Saxenda go under the skin of the belly, thigh or upper arm, and their labels say to change the spot with each dose456. FDA found no approved BPC-157 product in any country, so no label sets an injection site for it or for other unapproved peptides7. This page reports what the labels and regulators say; it is not a how-to.

26 sources · 9 min read · By the Pinc Peptide editors

Do peptide injections go under the skin or into a muscle?

Most approved peptide medicines are subcutaneous injections, which means they go into the layer of fat just under the skin48. The labels for Zepbound, Wegovy, Saxenda, Egrifta, Vyleesi and Forzinity all use this route4568910.

A few peptides are given into a vein or a muscle instead, by health professionals. Pitocin, the oxytocin drug used in childbirth, is given by drip into a vein in hospital, or as a shot into a muscle after the placenta is delivered11. Russia licenses thymalin for injection into a muscle12, and EU countries license Cerebrolysin for injection into a muscle or a vein13.

Afamelanotide, the approved form of melanotan I, is not injected at all: as Scenesse, it is a small implant that a health professional trained by the maker places under the skin just above the front of the hip bone14.

Where are approved peptide medicines injected?

Each label names its own body sites45. These are the sites in the US labels, product by product:

  • Tirzepatide, as Zepbound or Mounjaro: under the skin of the belly or thigh, or the back of the upper arm, where the labels say another person should give the injection415.
  • Semaglutide, as Wegovy or Ozempic: under the skin of the belly, thigh or upper arm516.
  • Liraglutide, as Saxenda or Victoza: under the skin of the belly, thigh or upper arm617.
  • Tesamorelin, as Egrifta SV or Egrifta WR: the belly only, moving between different areas of it918. The Egrifta SV label adds that it should not go into scar tissue, bruises or the navel18.
  • PT-141 (bremelanotide), as Vyleesi: under the skin of the belly or the front of the thigh, by autoinjector, avoiding the 2 inches around the belly button10.
  • SS-31 (elamipretide), as Forzinity: under the skin of the belly, at least 2 inches from the navel, or the outer thigh8.
  • Melanotan I (afamelanotide), as Scenesse: an implant inserted under the skin above the front of the hip bone by a trained health professional14.
  • Oxytocin, as Pitocin: a drip into a vein in hospital, or a shot into a muscle after delivery11.

Where a label allows more than one site, the site made little difference to how much drug reached the blood: levels were similar from the belly, thigh or upper arm for tirzepatide and semaglutide, and from the belly or thigh for bremelanotide and elamipretide45810.

The Zepbound label also says never to share a pen between patients, even if the needle is changed, because sharing can pass on blood-borne infections4.

Why do the labels say to rotate injection sites?

The GLP-1, tesamorelin and Forzinity labels all tell patients to change the injection spot with each dose45689.

Repeated injections in one spot can change the skin and the fat under it. The tirzepatide labels say rotating within the chosen area lowers the risk of lipodystrophy (pits in the skin or thickened skin) and localized cutaneous amyloidosis (skin with lumps)415. The Saxenda and Victoza labels give the same reason for rotating within one region, and list cutaneous amyloidosis among the problems reported since approval617.

The tesamorelin labels give a second reason: moving to different areas of the belly lowers the chance of injection-site reactions918.

How common are injection-site reactions?

An injection-site reaction is redness, itching, pain, swelling, hardening, bruising or a rash where the needle went in89. The labels report how often they happened in trials, from rare to almost universal:

  • Ozempic: 0.2% of patients in placebo-controlled trials16.
  • Wegovy: 1.4%, against 1% on placebo, in weight-loss trials in adults5.
  • Victoza: about 2% of adults in five diabetes trials; fewer than 0.2% stopped treatment because of them17.
  • Mounjaro: 3.2%, against 0.4% on placebo15.
  • Zepbound: 6% to 8% across the doses tested, against 2% on placebo4.
  • Vyleesi: 13.2%, against 8.4% on placebo; about 1% stopped treatment because of them10.
  • Saxenda: 13.9%, against 10.5% on placebo6.
  • Scenesse implant: 21%, against 10% with a dummy implant; the most common was discolored skin at the site, in 10%14.
  • Egrifta: 25%, against 14% on placebo, in the first 26 weeks9.
  • Forzinity: all 12 patients in its small crossover trial had a reaction at the site, against 8 of 12 while on placebo8.

The immune system plays a part. In seven Mounjaro trials, reactions affected 4.6% of adults who made antibodies against tirzepatide and 0.7% of those who did not15.

Where is BPC-157 injected, and other peptides with no label?

No label sets an injection site for BPC-157, because FDA found no approved BPC-157 product in any country7. FDA also found no human data on how the body handles it after injection under the skin7.

The same gap holds for other popular injectables. FDA’s 2026 review found no human data on TB-500 by any route19, and no published study that gave MOTS-c to people, by injection under the skin or otherwise20. Health Canada says unauthorized injectable peptides such as BPC-157, TB-500 and MOTS-c have not been assessed for safety, effectiveness or quality21.

In August 2026, FDA’s warning letters to peptide sellers cited a “peptide calculator”, a “peptide guide” and blog-style product comparisons as evidence that the products were drugs meant for people222324. Injection charts for these products, whoever publishes them, rest on no approved label.

What are the risks of injecting gray-market peptides?

A 2026 review in Missouri Medicine says products from online research-chemical suppliers are made outside the manufacturing rules that drugmakers must follow1. Because they usually arrive as freeze-dried powder that buyers mix themselves, it says, the risks of bacterial endotoxin (toxic material from bacteria), wrong doses and infections at the injection site are much higher1.

Health Canada warns that unauthorized injectable peptides can lead to infections, allergic reactions and other serious complications21. It adds that they can contain bacteria, fungi, endotoxins, or particles such as fibers, glass or plastic21. Our briefing collects lab tests of what is actually in the vials.

  • A clinician who runs a wellness clinic told NPR of seeing injection-site irritation and infections in people who had injected GHK-Cu bought online25.
  • In FDA’s adverse event reports, a woman injecting compounded BPC-157 and thymosin had 9 days of redness and swelling around the injection site7.
  • In July 2025, two women became critically ill after peptide injections at a longevity festival in Las Vegas26.

Our side-effects guide covers the harms beyond the skin, including contamination found by regulators21.

When does an injection site need a doctor?

Normal skin carries bacteria, and a break in the skin can let them cause an infection called cellulitis2. MedlinePlus, the US National Library of Medicine’s health site, lists these signs of a skin infection:

  • Redness or swelling that grows as the infection spreads, with warm, tender or painful skin2.
  • Tight, glossy, stretched-looking skin2.
  • Fever with chills and sweating2.
  • Pus or other drainage, which can mean an abscess, a pocket of pus in the skin3.
  • Blistering, or red streaks spreading from the area2.

MedlinePlus says to contact a health provider right away if you have symptoms of cellulitis, because untreated skin infections can spread to the blood23.

Allergic reactions are a separate emergency. The Zepbound label tells patients to stop and get medical help right away for swelling of the face, lips, tongue or throat, trouble breathing or swallowing, severe rash or itching, fainting or a very rapid heartbeat4.

Health Canada advises anyone who has used an unauthorized injectable peptide and feels unwell to contact a doctor, nurse practitioner or pharmacist21.

The evidence at a glance

TierBest human evidenceCompounds
ATwo or more large human trialsCagrilintide, Liraglutide, Mazdutide, Melanotan I (afamelanotide), Orforglipron, Oxytocin, PT-141 (bremelanotide), Retatrutide, Semaglutide, Survodutide, Tesamorelin, Thymosin alpha-1, Thymosin beta-4, Tirzepatide
BAt least one controlled human trialAOD-9604, BPC-157, Cerebrolysin, DSIP (emideltide), Epitalon, GHK-Cu, GHRP-2 (pralmorelin), GHRP-6, Glutathione, Gonadorelin, Hexarelin, Ipamorelin, Kisspeptin, LL-37, Melanotan II, MK-677 (ibutamoren), NAD+, Selank, Semax, Sermorelin, SS-31 (elamipretide), Thymalin, VIP (vasoactive intestinal peptide)
COnly small or uncontrolled human studiesCJC-1295
DAnimal studies onlyDihexa, KPV, MOTS-c, Pentadeca arginate (PDA), TB-500
ELab or anecdotal evidence onlyPEG-MGF

A tier grades the best human evidence for any use, not whether a compound is safe. Whether each one works for the use people take it for, and its legal status: the evidence table. How we grade: our method.

Questions people ask

Where do you inject BPC-157?

No label says, because FDA found no approved BPC-157 product in any country7. FDA also found no human data on how it is absorbed after injection under the skin7. Health Canada warns that unauthorized injectable peptides like it can cause infections and may be contaminated21.

Is it better to inject in the stomach or the thigh?

For approved drugs that allow both, the labels report similar blood levels from either site45810. Tesamorelin is the exception: its labels name the belly only918.

Can you inject tirzepatide in the arm?

The Zepbound and Mounjaro labels list the back of the upper arm, but say another person should give the injection there415.

Why do you have to rotate injection sites?

The labels say rotating lowers the risk of skin changes at the site, such as pits, thickened skin or lumps46. The tesamorelin labels add that it lowers the chance of injection-site reactions9.

Is a lump or redness after a peptide injection normal?

Redness, itching, swelling and hardened skin at the site are listed side effects of approved peptide injections, reported in 0.2% to 25% of patients depending on the drug916. Redness that keeps spreading, warmth, fever or pus can mean an infection, and MedlinePlus says to contact a health provider23.

Do peptide injections hurt?

Pain at the site is one of the injection-site reactions listed on the labels, and how often it happens varies by drug89. In the small Forzinity trial, 9 of 12 patients reported pain at the site, against 5 of 12 while on placebo8.

Go deeper

Sources

  1. 1Dangers of Injectable Peptides and Other Unregulated “Biohacking” Drugs Missouri Medicine, 2026. pubmed.ncbi.nlm.nih.gov
  2. 2Cellulitis MedlinePlus Medical Encyclopedia (U.S. National Library of Medicine), 1 Apr 2025. medlineplus.gov
  3. 3Skin abscess MedlinePlus Medical Encyclopedia (U.S. National Library of Medicine), 13 Oct 2024. medlineplus.gov
  4. 4ZEPBOUND (tirzepatide) injection, for subcutaneous use: prescribing information Eli Lilly and Company via DailyMed (U.S. National Library of Medicine), 28 Aug 2026. dailymed.nlm.nih.gov
  5. 5WEGOVY (semaglutide) injection and tablets: prescribing information (SPL version 19) Novo Nordisk via DailyMed (U.S. National Library of Medicine), 30 Jun 2026. dailymed.nlm.nih.gov
  6. 6SAXENDA (liraglutide) injection: prescribing information (SPL version 22) Novo Nordisk via DailyMed (U.S. National Library of Medicine), 15 Jun 2026. dailymed.nlm.nih.gov
  7. 7FDA Briefing Document, Pharmacy Compounding Advisory Committee meeting of July 23-24, 2026: BPC-157-related bulk drug substances U.S. Food and Drug Administration, 11 May 2026. fda.gov
  8. 8FORZINITY (elamipretide) injection prescribing information Stealth BioTherapeutics via DailyMed (U.S. National Library of Medicine), 10 Dec 2025. dailymed.nlm.nih.gov
  9. 9EGRIFTA WR (tesamorelin) for injection: prescribing information (revised 3/2025) Theratechnologies via DailyMed (U.S. National Library of Medicine), Mar 2025. dailymed.nlm.nih.gov
  10. 10VYLEESI (bremelanotide injection) prescribing information Cosette Pharmaceuticals via DailyMed (U.S. National Library of Medicine), 13 Nov 2025. dailymed.nlm.nih.gov
  11. 11PITOCIN (oxytocin injection, USP) prescribing information Par Health USA, LLC via DailyMed (U.S. National Library of Medicine), 21 May 2026. dailymed.nlm.nih.gov
  12. 12Тималин (Thymalin), lyophilizate for intramuscular injection 10 mg: instructions for use Vidal Russia drug reference, 25 Mar 2025. vidal.ru
  13. 13Article 57 product data (EMA/518502/2018, Rev.89; data as present in the Article 57 database on 21 September 2026) European Medicines Agency, 21 Sep 2026. ema.europa.eu
  14. 14SCENESSE (afamelanotide) implant prescribing information Clinuvel via DailyMed (U.S. National Library of Medicine), 11 May 2026. dailymed.nlm.nih.gov
  15. 15MOUNJARO (tirzepatide) injection, for subcutaneous use: prescribing information Eli Lilly and Company via DailyMed (U.S. National Library of Medicine), 27 Aug 2026. dailymed.nlm.nih.gov
  16. 16OZEMPIC (semaglutide) injection: prescribing information (SPL version 20) Novo Nordisk via DailyMed (U.S. National Library of Medicine), 10 Jun 2026. dailymed.nlm.nih.gov
  17. 17VICTOZA (liraglutide) injection: prescribing information (SPL version 31) Novo Nordisk via DailyMed (U.S. National Library of Medicine), 17 Nov 2025. dailymed.nlm.nih.gov
  18. 18EGRIFTA SV (tesamorelin) for injection: prescribing information (revised 2/2024) Theratechnologies via DailyMed (U.S. National Library of Medicine), Feb 2024. dailymed.nlm.nih.gov
  19. 19FDA Briefing Document, Pharmacy Compounding Advisory Committee meeting of July 23-24, 2026: TB-500-related bulk drug substances U.S. Food and Drug Administration, 15 May 2026. fda.gov
  20. 20July 23-24, 2026, Meeting of the Pharmacy Compounding Advisory Committee – FDA Briefing Document for MOTS-c-Related Bulk Drug Substances (MOTS-c (free base) and MOTS-c acetate) U.S. Food and Drug Administration, 11 May 2026. fda.gov
  21. 21Think twice before injecting peptides bought online: unauthorized products can seriously harm you (RA-81874) Health Canada, 9 Apr 2026. recalls-rappels.canada.ca
  22. 22Warning letter to Royal Peptides LLC (MARCS-CMS 734884) U.S. Food and Drug Administration, 24 Aug 2026. fda.gov
  23. 23Warning letter to NuScience Peptides LLC (MARCS-CMS 733652) U.S. Food and Drug Administration, 24 Aug 2026. fda.gov
  24. 24Warning letter to Peptide Partners LLC (MARCS-CMS 735063) U.S. Food and Drug Administration, 24 Aug 2026. fda.gov
  25. 25The copper peptide trend has gone from creams to injections — ahead of the science NPR, 7 Sep 2026. npr.org
  26. 26A Las Vegas Festival Promised Ways to Cheat Death. Two Attendees Left Fighting for Their Lives. ProPublica, 29 Jul 2025. propublica.org

Not medical advice. Nothing here recommends using any product. How we grade evidence · Report an error.