Eli Lilly Tests Whether Weight-Loss Drug Retatrutide Alters Heart Medication Levels
A Phase 1 trial examines if the triple-agonist GLP-1 drug retatrutide changes how the body processes the beta-blocker metoprolol.
Summary
Retatrutide is a powerful new triple-agonist drug targeting GLP-1, GIP, and glucagon receptors, showing remarkable results for weight loss and metabolic health. Like other GLP-1 drugs, it may slow gastric emptying, which can alter how the body absorbs and processes other medications. This Phase 1 trial by Eli Lilly investigated whether retatrutide changes the pharmacokinetics — meaning the absorption, distribution, and elimination — of metoprolol, a widely prescribed beta-blocker used for high blood pressure and heart disease. Since many patients who might use retatrutide also take cardiovascular medications like metoprolol, understanding potential drug interactions is critical for safe prescribing. The trial enrolled healthy participants and has been completed, though full results have not yet been published.
Detailed Summary
As next-generation GLP-1 receptor agonists move toward widespread clinical use, understanding their potential to alter the pharmacokinetics of co-administered drugs becomes a critical safety question. Retatrutide, developed by Eli Lilly, is a triple agonist targeting GLP-1, GIP, and glucagon receptors simultaneously — a mechanism that produces substantial weight loss and metabolic improvements. However, like other drugs in this class, retatrutide may delay gastric emptying, which can meaningfully change how orally taken medications are absorbed into the bloodstream.
This Phase 1 study (NCT06808802) was designed specifically to measure whether retatrutide affects the pharmacokinetics of metoprolol, a commonly used beta-blocker prescribed for hypertension, heart failure, and cardiac arrhythmias. Metoprolol was chosen as a probe drug because it is sensitive to changes in gastric emptying and absorption rate, making it a useful marker for detecting drug-drug interactions caused by GLP-1-class agents.
The trial enrolled healthy participants and has been completed as of early 2025. However, results have not been publicly reported in full, so specific pharmacokinetic parameters — such as changes in peak plasma concentration (Cmax) or area under the curve (AUC) — remain unavailable from the abstract alone.
The clinical implications are significant. Millions of people with obesity or type 2 diabetes — the primary populations likely to receive retatrutide — also have cardiovascular comorbidities requiring beta-blocker therapy. If retatrutide meaningfully alters metoprolol exposure, dose adjustments or additional monitoring may be warranted when prescribing these agents together.
This study represents standard regulatory due diligence before broader approval, but the findings will carry real-world weight for cardiologists and primary care physicians managing complex patients on multiple medications. Full publication of results is needed before definitive clinical guidance can be issued.
Key Findings
- Phase 1 trial tested whether retatrutide, a triple GLP-1/GIP/glucagon agonist, alters metoprolol blood levels in healthy adults.
- Metoprolol was used as a probe drug because its absorption is sensitive to gastric emptying changes caused by GLP-1 agents.
- Study is completed but full results are not yet publicly available from the registered abstract.
- Findings will directly inform prescribing safety for the large overlap of obesity and cardiovascular disease patients.
- Sponsored by Eli Lilly as part of retatrutide's broader drug interaction profiling ahead of potential approval.
Methodology
This was a Phase 1 pharmacokinetic drug-drug interaction study in healthy participants, sponsored by Eli Lilly. The design measured metoprolol pharmacokinetic parameters before and during retatrutide administration. The trial is registered on ClinicalTrials.gov (NCT06808802) and is listed as completed as of February 2025.
Study Limitations
The summary is based on the abstract only, as the full trial results have not been published; no pharmacokinetic data or outcomes are available for review. The study was conducted in healthy participants, which may not reflect pharmacokinetic interactions in patients with obesity, diabetes, or cardiovascular disease. Generalizability to other beta-blockers or cardiovascular drugs cannot be assumed from this single probe-drug study.
Enjoyed this summary?
Get the latest longevity research delivered to your inbox every week.