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Retatrutide and GHK-Cu Together: What Is Known

Retatrutide and GHK-Cu taken together: what each one is, how each is regulated, and what is known about combining them.

Medically reviewed by Juan Pablo Frías, MD · · DisclosureUpdated
GLP-1 / GIP / glucagon triple agonistInvestigational · phase 3RetatrutideInvestigational triple GIP, GLP-1 and glucagon receptor agonist, not FDA-approved; a phase 3 TRIUMPH trial reported mean weight change of -25.0% at the 12-mg dose versus -3.9% with placebo.[1]GLP-1 & metabolicCopper tripeptideInjectable off Category 2 (Apr 2026)GHK-CuCopper tripeptide with mostly topical or cosmetic human data; a small randomized laser-resurfacing study found no statistically significant differences between groups for earlier resolution of erythema.[10]Skin & hair
Interaction notes

Timing, interactions and safety

Evidence for the combination

No studies tested these together (PubMed search: 0 results, 2 Oct 2026).

Neither is FDA approved for use in people, and we have no sourced data on combining them.
Each component

Side by side

Showing 11 of 13 fields where the two differ. PCAC vote, Jul 2026, Evidence strength are the same or both unknown.

FieldRetatrutideGHK-Cu
ClassGLP-1 / GIP / glucagon triple agonistCopper tripeptide
Also calledreta, GLP-3, LY3437943copper peptide, copper tripeptide-1, GHK
CategoryGLP-1 & metabolicSkin & hair
FDA statusInvestigational · phase 3Injectable off Category 2 (Apr 2026)
WADAProhibited by WADA (S0)Retatrutide is not named, and GLP-1/amylin class agonists are not listed. But it is an investigational drug with no approval in the sources we reviewed, and S0 prohibits drugs under clinical development that no authority has approved. If it is approved somewhere this would change.WADA status unclearGHK-Cu: This is not named on the 2026 list. The catch-all class S0 prohibits any drug with no approval anywhere for human use, so it would be banned if no health authority has approved it, but we have not verified that for this substance.
Half-lifeapproximately 6 dayssubcutaneous · Lancet 2022, PMID 36354040No published half-life foundPubMed search, 2 Oct 2026
Human studies we summarised11 human (11 randomized or controlled) of 16 summarised4 human (2 randomized or controlled) of 14 summarised
Typical study doses
Vial sizes sold5 mg, 10 mg, 12 mg, 15 mg, 20 mg, 24 mg, 30 mg, 36 mg, 40 mg, 50 mg, 60 mg50 mg, 100 mg, 200 mg
US searches per month823,000 · +172% searches234,100 · +340% searches
Named in FDA warning letters, 2026Yes (24 Aug 2026; 31 Mar 2026)Not in the letters we track

What people search

  • reta and ghkcu880/mo
  • reta ghk cu260/mo
  • ghk cu and reta90/mo
  • ghk cu reta50/mo
  • reta and ghk cu together20/mo
  • reta with ghk cu10/mo

US monthly searches, Google Keyword Planner, Oct 2026. Shown so you can see which questions this page answers.

Sources

  1. 1Retatrutide phase 3 TRIUMPH-1 results publishedNEJM (PubMed 42814954) · 2026pubmed.ncbi.nlm.nih.govAccessed 2 Oct 2026
  2. 2FDA warning letters to five research-peptide sellersFDA warning letter (NuScience Peptides; 1 of 5) · 2026fda.govAccessed 2 Oct 2026
  3. 3Eli Lilly sues six retatrutide sellersEli Lilly (press release) · 2026investor.lilly.comAccessed 2 Oct 2026
  4. 4FDA gives notice that 12 peptides will be removed from Category 2 (nominations withdrawn)FDA · 2026fda.govAccessed 2 Oct 2026
  5. 5Seven FDA warning letters to online sellers of GLP-1 productsFDA warning letter (Gram Peptides; 1 of 7) · 2026fda.govAccessed 2 Oct 2026
  6. 6World Anti-Doping Code International Standard Prohibited List 2026World Anti-Doping Agency · 2026wada-ama.orgAccessed 2 Oct 2026
  7. 7LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial.Lancet (London, England) · 2022PMID 36354040Accessed 2 Oct 2026
  8. 8Retatrutide-Associated Improvements in Cardiovascular Risk Biomarkers in Adults With Obesity With or Without Type 2 Diabetes.Diabetes, obesity & metabolism · 2026PMID 42608321Accessed 2 Oct 2026
  9. 9Effects of retatrutide on body composition in people with type 2 diabetes: a substudy of a phase 2, double-blind, parallel-group, placebo-controlled, randomised trial.The lancet. Diabetes & endocrinology · 2025PMID 40609566Accessed 2 Oct 2026
  10. 10Effects of topical copper tripeptide complex on CO2 laser-resurfaced skin.Archives of facial plastic surgery · 2006PMID 16847171Accessed 2 Oct 2026
  11. 11Tripeptide-copper complex GHK-Cu (II) transiently improved healing outcome in a rat model of ACL reconstruction.Journal of orthopaedic research : official publication of the Orthopaedic Research Society · 2015PMID 25731775Accessed 2 Oct 2026
  12. 12PubMed search: ("GHK-Cu"[tiab] OR GHK[tiab] OR "copper tripeptide"[tiab] OR "copper peptide"[tiab] OR "copper peptides"[tiab] OR "glycyl-L-histidyl-L-lysine"[tiab] OR "glycyl-histidyl-lysine"[tiab] OR "Gly-His-Lys"[tiab]) (431 results)PubMed · 2026pubmed.ncbi.nlm.nih.govAccessed 2 Oct 2026
  13. 13PubMed search: ("GHK-Cu"[tiab] OR GHK[tiab] OR "copper tripeptide"[tiab] OR "copper peptide"[tiab] OR "copper peptides"[tiab] OR "glycyl-L-histidyl-L-lysine"[tiab] OR "glycyl-histidyl-lysine"[tiab] OR "Gly-His-Lys"[tiab]) AND (humans[mh] OR patients[tiab] OR volunteers[tiab]) (150 results)PubMed · 2026pubmed.ncbi.nlm.nih.govAccessed 2 Oct 2026
  14. 14PubMed search: ("GHK-Cu"[tiab] OR GHK[tiab] OR "copper tripeptide"[tiab] OR "copper peptide"[tiab] OR "copper peptides"[tiab] OR "glycyl-L-histidyl-L-lysine"[tiab] OR "glycyl-histidyl-lysine"[tiab] OR "Gly-His-Lys"[tiab]) AND (randomized[tiab] OR clinical trial[pt] OR split-face[tiab]) (8 results)PubMed · 2026pubmed.ncbi.nlm.nih.govAccessed 2 Oct 2026
  15. 15PubMed search: ("GHK-Cu"[tiab] OR GHK[tiab] OR "copper tripeptide"[tiab] OR "copper peptide"[tiab] OR "copper peptides"[tiab] OR "glycyl-L-histidyl-L-lysine"[tiab] OR "glycyl-histidyl-lysine"[tiab] OR "Gly-His-Lys"[tiab]) AND (wound[tiab] OR hair[tiab] OR skin[tiab] OR wrinkle*[tiab]) (123 results)PubMed · 2026pubmed.ncbi.nlm.nih.govAccessed 2 Oct 2026
  16. 16PubMed search: ("GHK-Cu"[tiab] OR GHK[tiab] OR "copper tripeptide"[tiab] OR "copper peptide"[tiab] OR "copper peptides"[tiab] OR "glycyl-L-histidyl-L-lysine"[tiab] OR "glycyl-histidyl-lysine"[tiab] OR "Gly-His-Lys"[tiab]) AND (half-life[tiab] OR pharmacokinetic*[tiab]) (2 results)PubMed · 2026pubmed.ncbi.nlm.nih.govAccessed 2 Oct 2026
  17. 17PubMed search: ("GHK-Cu"[tiab] OR GHK[tiab] OR "copper tripeptide"[tiab] OR "copper peptide"[tiab] OR "copper peptides"[tiab] OR "glycyl-L-histidyl-L-lysine"[tiab] OR "glycyl-histidyl-lysine"[tiab] OR "Gly-His-Lys"[tiab]) AND (rat[tiab] OR mice[tiab] OR rats[tiab] OR animal[tiab]) (80 results)PubMed · 2026pubmed.ncbi.nlm.nih.govAccessed 2 Oct 2026
  18. 18PubMed search: ("GHK-Cu"[tiab] OR "copper tripeptide"[tiab] OR "copper peptide"[tiab] OR "copper peptides"[tiab] OR "glycyl-L-histidyl-L-lysine"[tiab] OR "glycyl-histidyl-lysine"[tiab] OR "Gly-His-Lys"[tiab]) AND (facial[tiab] OR cream[tiab] OR photodamage[tiab] OR volunteers[tiab] OR women[tiab]) (6 results)PubMed · 2026pubmed.ncbi.nlm.nih.govAccessed 2 Oct 2026
  19. 19PubMed search: ("GHK-Cu"[tiab] OR "copper tripeptide"[tiab] OR "copper peptide"[tiab] OR "copper peptides"[tiab] OR "glycyl-L-histidyl-L-lysine"[tiab] OR "glycyl-histidyl-lysine"[tiab] OR "Gly-His-Lys"[tiab]) AND (hair[tiab] OR alopecia[tiab]) (16 results)PubMed · 2026pubmed.ncbi.nlm.nih.govAccessed 2 Oct 2026
  20. 20PubMed search: ("GHK-Cu"[tiab] OR GHK[tiab] OR "copper tripeptide"[tiab] OR "copper peptide"[tiab] OR "copper peptides"[tiab] OR "glycyl-L-histidyl-L-lysine"[tiab] OR "glycyl-histidyl-lysine"[tiab] OR "Gly-His-Lys"[tiab]) AND (retatrutide[tiab] OR LY3437943[tiab])PubMed · 2026pubmed.ncbi.nlm.nih.govAccessed 2 Oct 2026

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