Retatrutide Interactions: What the Trials Excluded
Two registered retatrutide interaction studies have no posted results. What the TRIUMPH and TRANSCEND protocols excluded and what the GLP-1 labels say.
Research use only. This page provides scientific background and community-report context. Every compound sold here is supplied strictly for in-vitro research. Nothing on this page is a protocol, a recommendation, or medical advice.
TL;DR: interaction studies exist, but results are missing
The question people actually type: does retatrutide interact with other medications, and who did the trials exclude?
What the published data say: a retatrutide paper reports delayed gastric emptying; the registered interaction studies have no posted results. [PMID 37311727; NCT05445232; NCT06808802]
What the documented search did not identify: no published retatrutide interaction findings for the specific medicines named below in the PubMed and ClinicalTrials.gov searches dated 12 September 2026. Trial exclusions cannot establish compatibility.
What research communities report: In the Reddit corpus we track, 1,940 question posts in 12 months and 62 in the 4 to 12 September 2026 window matched this pattern. These are reports, not evidence of interaction frequency.
What interaction studies were registered for retatrutide?
The registries list a drug-cocktail study and a metoprolol study, both completed without posted results at the 12 September 2026 retrieval. The cocktail study enrolled 32 participants and examined oral midazolam, warfarin and caffeine with subcutaneous retatrutide; it completed on 2023-02-24. The metoprolol study enrolled 30 healthy participants and completed on 2025-04-15. [NCT05445232; NCT06808802]
The cocktail protocol excluded participants already receiving midazolam, warfarin, or inhibitors or inducers of CYP1A2, CYP2C9 or CYP3A4. Those restrictions describe the experiment, not an observed interaction result. PubMed searches on 12 September 2026 for retatrutide AND midazolam, retatrutide AND warfarin and retatrutide AND metoprolol each returned 0 hits; no published report of either study was located. [NCT05445232; NCT06808802]
What do the approved labels say about other medicines?
The approved tirzepatide and semaglutide labels provide compound-specific findings, not a retatrutide interaction list. PeptidesDirect does not sell tirzepatide. PeptidesDirect does not sell semaglutide.
Retatrutide has a gastric-emptying publication, but its PubMed record has no abstract. It cannot supply medicine-specific absorption estimates here. [PMID 37311727] The ZEPBOUND prescribing information describes potential changes in oral medicine absorption through delayed gastric emptying. Its oral-contraceptive study reported changes in peak concentrations and total exposure, and the MOUNJARO label contains a 4-week barrier or non-oral contraception instruction after initiation and after each dose step. These are tirzepatide label findings; they do not establish a retatrutide contraception rule. [ZEPBOUND PI 7.2, 12.3; MOUNJARO PI 7.2]
By contrast, the OZEMPIC label reports no clinically relevant interaction for the evaluated medicines: metformin, an oral contraceptive, warfarin, digoxin and atorvastatin. That finding concerns semaglutide and those tested medicines. [OZEMPIC PI 7.2, 12.3]
The labels also identify hypoglycemia risk with insulin or insulin secretagogues. The ZEPBOUND label describes severe gastrointestinal disease, including severe gastroparesis, as unstudied, and advises against coadministration with another GLP-1 receptor agonist. Its contraindications name personal or family medullary thyroid carcinoma (MTC) and multiple endocrine neoplasia type 2 (MEN 2); the OZEMPIC label names the same thyroid conditions. These label statements are not retatrutide findings. [ZEPBOUND PI 7.1, 5.2, 1, 4; OZEMPIC PI 7.1, 5.1]
Who did the retatrutide trials exclude?
Exclusions differed across protocols and substudies; they define whose outcomes the trials could examine. The table compares selected eligibility restrictions, not adverse-event rates.
- Selected exclusions
- Trial exclusions: weight-changing medicines; pancreatitis; symptomatic gallbladder disease; HIV; eGFR below 45 mL/min/1.73 m²
- Comparator or scope
- TRANSCEND-T2D-1 instead used eGFR <15 mL/min/1.73 m² [NCT06354660]
- Selected exclusions
- Trial exclusions: diabetes; pancreatitis; MTC or MEN 2; weight loss drugs within 90 days
- Comparator or scope
- Sleep apnea addenda had additional medicine exclusions
- Selected exclusions
- Hypnotics, mirtazapine, opioids, trazodone and zonisamide within 3 months
- Comparator or scope
- TRIUMPH-1 also listed wakefulness stimulants within 3 months
- Selected exclusions
- Trial exclusions: specified cardiac events or stroke within 90 days
- Comparator or scope
- Different scope from joint-related exclusions
- Selected exclusions
- Steroid joint injections within 90 days
- Comparator or scope
- Other joint procedures within 6 months
- Selected exclusions
- Clinically significant gastric-emptying abnormality; weight reduction medicines or remedies within 90 days
- Comparator or scope
- Also pancreatitis, MTC or MEN 2
The phase 2 obesity registry also excluded recent depression or other mental illness. The phase 2 diabetes trial registry separately named autoimmune abnormalities, exemplified by lupus or rheumatoid arthritis. Neither wording establishes a studied interaction with antidepressants or thyroid replacement. MTC and MEN 2 are distinct from autoimmune thyroiditis; the latter cannot be inferred from those named thyroid exclusions. [NCT04881760; NCT04867785]
Further eligibility context appears in Who the Trials Enrolled, and Who They Excluded.
Which co-medications did protocols allow?
Some diabetes protocols explicitly included background glucose-lowering medicines. The phase 2 diabetes study allowed stable metformin. TRANSCEND-T2D-2 studied retatrutide with metformin, with or without an SGLT2 inhibitor; another phase 3 record studied background basal insulin, with or without metformin and/or an SGLT2 inhibitor. Inclusion documents a study design, not compatibility with every medicine in those classes. [NCT04867785; NCT06260722; NCT06297603]
What remains unanswered by human studies?
The following PubMed and ClinicalTrials.gov search results were retrieved on 12 September 2026; no published retatrutide study was located for these combinations, so there is no human interaction data to cite.
PubMed searches returned 0 for retatrutide AND (oral contraceptive OR contraception), retatrutide AND levothyroxine, retatrutide AND isotretinoin, retatrutide AND (inflammatory bowel disease OR Crohn OR colitis) and retatrutide AND (antiviral OR PrEP OR tenofovir). ClinicalTrials.gov searches retatrutide levothyroxine, retatrutide isotretinoin and retatrutide inflammatory bowel also returned 0. Its retatrutide contraceptive search found a postmenopausal study, not an interaction study. [NCT06039826]
PubMed retatrutide AND (Hashimoto OR thyroiditis) returned 3 reviews or a network meta-analysis; retatrutide AND (SSRI OR antidepressant OR sertraline) returned 1 pharmacotherapy review. Neither search located a published retatrutide study on autoimmune thyroiditis or SSRIs. [12 September 2026; PMID 40042613, 41393574, 42688617, 39096466]
No marketing authorization was located in the FDA and EMA sources checked on 12 September 2026: Drugs@FDA openfda.generic_name:"retatrutide" returned 0 records, and EMA/201150/2026 contained no match for r[eé]tatrut|LY3437943. No approved retatrutide label with an interaction section was located in these two sources on 12 September 2026. For the separate reproductive-evidence question, see retatrutide and contraception.
Products mentioned
Retatrutide (LY3437943) is a synthetic 39-amino-acid peptide that acts on three receptors at once: GLP-1, GIP and glucagon. Supplied as a lyophilized powder for in-vitro research, with a batch-specific third-party certificate of analysis.
Sources
- ClinicalTrials.gov, retrieved 12 September 2026. Cocktail interaction study, NCT05445232; metoprolol PK study, NCT06808802.
- Urva, 2023. The novel GIP, GLP-1 and glucagon receptor agonist retatrutide delays gastric emptying. Diabetes Obes Metab 25(9):2784-2788. PMID 37311727.
- ZEPBOUND US prescribing information, retrieved 12 September 2026. Sections 1, 4, 5.2, 7.1, 7.2, 12.3. Setid 487cd7e7-434c-4925-99fa-aa80b1cc776b; FDA 217806Orig1s020lbl.pdf.
- MOUNJARO US prescribing information, retrieved 12 September 2026. Section 7.2. Setid d2d7da5d-ad07-4228-955f-cf7e355c8cc0.
- OZEMPIC US prescribing information, retrieved 12 September 2026. Sections 5.1, 7.1, 7.2, 12.3. Setid adec4fd2-6858-4c99-91d4-531f5f2a2d79.
- ClinicalTrials.gov, retrieved 12 September 2026. Phase 2 obesity, NCT04881760; phase 2 diabetes, NCT04867785.
- ClinicalTrials.gov, retrieved 12 September 2026. TRIUMPH-1, NCT05929066; TRIUMPH-2, NCT05929079; TRIUMPH-3, NCT05882045; TRIUMPH-4, NCT05931367.
- ClinicalTrials.gov, retrieved 12 September 2026. TRANSCEND-T2D-1, NCT06354660; TRANSCEND-T2D-2, NCT06260722; basal insulin background study, NCT06297603; postmenopausal phase 1 study, NCT06039826.
- PubMed and ClinicalTrials.gov, searches dated 12 September 2026. Absence searches reproduced above; review-only hits PMID 40042613, 41393574, 42688617, 39096466.
- FDA Drugs@FDA, data last updated 2026-09-11; EMA, Applications for new human medicines under evaluation by the CHMP, 2026-09-04, EMA/201150/2026. Searches dated 12 September 2026.
- PeptidesDirect, 2026. Reddit question corpus: question-posts.jsonl and delta2/questions.json; interaction, co-medication and trial-exclusion patterns.
Research use only. Retatrutide is supplied strictly for in-vitro laboratory research, not for human or animal administration. Nothing here is a protocol, a recommendation, or medical advice.
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