Interaction Checker

How this tool works · sources read September 30, 2026 · Grey Peptides Editorial Board

What the checker does

Add up to six compounds and the checker looks up every pair among them in a table of 38 pairs, then arranges the compounds by the timing note each carries. Each pair has one of four ratings. Conflict means a drug label advises against the combination, or the two duplicate one mechanism. Caution means they share a receptor or pathway, or one of them lacks the evidence the pairing assumes. Complementary means their mechanisms differ; it does not mean a study showed the combination works better, and each such rating says whether any study has tested the pair. Neutral means nothing in the pair's mechanisms or labels points either way. A pair outside the table shows "No Data Available" and is filed under neutral, which here means no data, not safe.

The table's 38 pairs: 6 conflict, 4 caution, 20 complementary and 8 neutral. The flagged ones:

What each rating rests on

The strongest ratings come from drug labels. Wegovy's label says that combining semaglutide with other semaglutide products or with any other GLP-1 receptor agonist is not recommended,¹ and Zepbound's says the same of tirzepatide with any GLP-1 receptor agonist.² Those two sentences are why every pairing of semaglutide, tirzepatide and retatrutide is a conflict.

For almost every other pair the honest basis is mechanism alone. Two GHRH analogs, such as CJC-1295 and sermorelin, act on one receptor, so combining them adds no second mechanism; two melanocortin agonists do the same. For the research peptides, no study has given any of these pairs to people, and each rating now says so. Where a compound's own evidence undercuts the pairing, the rating says that instead: AOD-9604's largest trial found no significant weight loss, and the paper linking dihexa to the HGF/c-Met pathway has been retracted, both as recorded in their encyclopedia entries.

The timing notes

Each compound carries a timing note, and each note says where it comes from. Some come from labels: semaglutide and tirzepatide are taken once weekly at any time of day, with or without meals;^3,4 Vyleesi is injected as needed at least 45 minutes before anticipated sexual activity;⁵ FORZINITY is given at the same time each day;⁶ and EGRIFTA SV's label sets a once-daily dose without a time of day.⁷ The rest, such as "bedtime, empty stomach" for growth hormone secretagogues, are community conventions, marked as such, and the schedule view that groups compounds by these notes is only as good as the notes.

What it does not check

The checker covers pairs among 23 peptides. It does not cover their interactions with prescription medicines, which is where the labelled interactions of approved peptides actually sit. GLP-1 medicines slow stomach emptying, and tirzepatide's labels tell people who use oral contraceptives to switch to a non-oral method, or add a barrier method, for 4 weeks after starting and after each dose increase.⁴ Semaglutide taken with insulin or a sulfonylurea raises the risk of low blood sugar, and its label advises considering a lower dose of those drugs.³ Our guide to GLP-1 drug interactions covers these, and a full interaction matrix across the encyclopedia is being built with a source for every cell.

Reading the results

• "Complementary" is not "proven". It describes mechanisms. No study has tested most complementary pairs in people.
• "Not reviewed" and "neutral" are not "safe". An absence of data is not evidence of safety.
• Two GLP-1 medicines are never a stack. The labels advise against it, whichever brands are involved.

Mixing in one syringe is a different question

The ratings here are for taking two products separately. Whether they can share a syringe is a separate question, and the labels answer it for GLP-1 medicines used with insulin: separate injections, never mixed.^8,9 For research peptides no compatibility data exist at all. Our mixing guide sets out what the labels, USP's compounding rules and the published literature say.

Sources

1. Novo Nordisk. WEGOVY (semaglutide) injection and tablets, US prescribing information: coadministration with other semaglutide-containing products or with any other GLP-1 receptor agonist is not recommended. DailyMed version of June 30, 2026, read September 30, 2026.
2. Eli Lilly and Company. ZEPBOUND (tirzepatide) injection, US prescribing information: coadministration with other tirzepatide-containing products or with any GLP-1 receptor agonist is not recommended. DailyMed version of September 2, 2026, read September 30, 2026.
3. Novo Nordisk. OZEMPIC (semaglutide) injection, US prescribing information: once weekly at any time of day, with or without meals; when initiating with an insulin secretagogue or insulin, consider reducing their dose to reduce the risk of hypoglycemia. DailyMed version of June 10, 2026, read September 30, 2026.
4. Eli Lilly and Company. MOUNJARO (tirzepatide) injection, US prescribing information: once weekly at any time of day, with or without meals; advise patients using oral hormonal contraceptives to switch to a non-oral method, or add a barrier method, for 4 weeks after initiation and after each dose escalation. DailyMed version of September 2, 2026, read September 30, 2026.
5. Cosette Pharmaceuticals. VYLEESI (bremelanotide) injection, US prescribing information: 1.75 mg as needed at least 45 minutes before anticipated sexual activity; transient increases in blood pressure; nausea in 40% of patients. DailyMed version of November 18, 2025, read September 30, 2026.
6. Stealth BioTherapeutics. FORZINITY (elamipretide) injection, US prescribing information: 40 mg once daily; patients should receive the dose at the same time each day. DailyMed version of December 12, 2025, read September 30, 2026.
7. Theratechnologies Inc. EGRIFTA SV (tesamorelin) for injection, US prescribing information: 1.4 mg injected subcutaneously once daily. DailyMed version of July 31, 2026, read September 30, 2026.
8. Novo Nordisk. OZEMPIC (semaglutide) injection, US prescribing information, section 2: when using OZEMPIC with insulin, administer as separate injections and never mix the products. DailyMed version of June 10, 2026, read September 30, 2026.
9. Eli Lilly and Company. MOUNJARO (tirzepatide) injection, US prescribing information, section 2: when using MOUNJARO with insulin, administer as separate injections and never mix. DailyMed version of September 2, 2026, read September 30, 2026.

This explainer describes how the tool works and what its numbers rest on. It is not medical advice and does not recommend any dose or product.