Retatrutide for Heart Failure: Evidence Summary and Off-Label Status

What Is Retatrutide and Why Does It Matter for Heart Failure?

Retatrutide is an investigational once-weekly subcutaneous peptide that simultaneously activates the glucose-dependent insulinotropic polypeptide (GIP) receptor, the glucagon-like peptide-1 (GLP-1) receptor, and the glucagon receptor. That triple-agonist profile separates it from approved agents such as semaglutide (GLP-1 only) or tirzepatide (GIP/GLP-1 dual). Heart failure is not among any of its indications because no indication has been approved.

Interest in retatrutide for heart failure flows from two streams of evidence: the profound weight loss it produces in obesity trials and the cardiovascular outcomes already demonstrated by GLP-1 receptor agonists in the same receptor class.

The Triple-Agonist Pharmacology

GLP-1 receptor activation reduces systemic inflammation and improves endothelial function [1]. Glucagon receptor co-activation increases cardiac output acutely and promotes natriuresis [2]. GIP receptor stimulation may reduce adipose tissue inflammation, a known driver of heart failure with preserved ejection fraction (HFpEF) [3]. Whether these three mechanisms add up to a net cardiac benefit in humans with established heart failure has not been tested in a completed, adequately powered trial.

The Weight Reduction Rationale

Obesity is present in more than 80% of HFpEF patients [4]. In the Phase 2 SURMOUNT-adjacent NCT04881760 trial (N=338), retatrutide 12 mg produced a mean body weight reduction of 17.5% at 24 weeks, rising to 22.8% at 48 weeks, compared with 1.6% for placebo (P<0.001) [5]. Weight reduction of that magnitude has been associated with improved Kansas City Cardiomyopathy Questionnaire (KCCQ) scores and reduced NT-proBNP in HFpEF patients treated with semaglutide in the STEP-HFpEF trial [6]. Extrapolating that chain of evidence to retatrutide is biologically reasonable but remains unproven.

FDA Approval Status and the Legal Off-Label Framework

Retatrutide holds no FDA approval. Eli Lilly submitted Phase 2 data to support Phase 3 design, and Phase 3 obesity trials are ongoing as of mid-2025 [7]. Prescribing retatrutide for any purpose in the United States requires compounded formulations or participation in a clinical trial, since no commercial product exists.

What Off-Label Means in Practice

The FDA does not prohibit physicians from prescribing approved drugs off-label, but retatrutide is not yet an approved drug at all. Compounded retatrutide has appeared in telehealth channels following the FDA's semaglutide and tirzepatide shortage designations, but those shortage-based compounding permissions apply specifically to the listed drugs, not to unapproved investigational compounds [8]. Clinicians considering compounded retatrutide should review FDA's current guidance on 503A and 503B compounding pharmacies before prescribing [8].

Liability and Informed Consent Considerations

Using any investigational agent outside a clinical trial places the full prescribing liability on the ordering physician. Informed consent should document the absence of FDA approval, the GRADE Very Low evidence level for heart failure specifically, the unknown long-term cardiovascular safety profile, and the availability of approved alternatives.

The Evidence Base: What Trials Actually Tell Us

No completed randomized controlled trial has evaluated retatrutide as a treatment for heart failure as a primary endpoint. The evidence that exists comes from three sources: Phase 2 metabolic trials with cardiac biomarker secondary endpoints, mechanistic studies, and extrapolation from the GLP-1 class literature.

Phase 2 Obesity and T2D Trials

The NCT04881760 Phase 2 trial enrolled 338 adults with obesity (BMI ≥27 with at least one weight-related comorbidity) or overweight. Participants were randomized to retatrutide 1 mg, 4 mg, 8 mg, or 12 mg once weekly or placebo for 48 weeks [5]. The primary endpoint was percent change in body weight. Cardiac biomarkers were pre-specified secondary endpoints.

At 48 weeks, the 12 mg arm showed:

• Mean body weight reduction: 22.8% vs. 1.6% placebo
• Systolic blood pressure reduction: 7.2 mmHg vs. 1.8 mmHg placebo
• Heart rate change: +2.6 bpm (a glucagon-receptor-mediated effect, potentially relevant in heart failure patients on rate-limiting agents)
• NT-proBNP change: not published in the primary paper; sub-analysis data are pending

The heart rate increase warrants attention. Glucagon receptor agonism raises resting heart rate, which could worsen symptoms in heart failure patients with reduced ejection fraction (HFrEF), particularly those already at risk for tachycardia-mediated cardiomyopathy [5].

GLP-1 Class Cardiovascular Outcomes: The Closest Analogy

Because no retatrutide cardiovascular outcomes trial exists, the best available analogy is the LEADER trial of liraglutide (N=9,340), which showed a 13% relative risk reduction in major adverse cardiovascular events (MACE) at 3.8-year median follow-up (HR 0.87, 95% CI 0.78 to 0.97, P<0.001 for non-inferiority and P=0.01 for superiority) [9]. Semaglutide data in HFpEF are more directly relevant.

STEP-HFpEF: The Proof-of-Concept for the Class

In STEP-HFpEF (N=529), adults with HFpEF and BMI ≥30 were randomized to semaglutide 2.4 mg weekly or placebo for 52 weeks [6]. The dual primary endpoint of KCCQ-CSS score and body weight showed:

• KCCQ-CSS improvement: 16.6 points semaglutide vs. 8.7 points placebo (estimated difference 7.8 points, P<0.001)
• Body weight reduction: 13.3% semaglutide vs. 2.6% placebo (P<0.001)
• 6-minute walk distance improvement: 21.5 m semaglutide vs. 1.2 m placebo

The New England Journal of Medicine editorial accompanying STEP-HFpEF stated: "These results provide the strongest evidence to date that a GLP-1 receptor agonist can improve symptoms and physical limitations in patients with HFpEF and obesity" [6]. Retatrutide's GLP-1 receptor component could theoretically produce similar or greater effects, but this has not been tested.

Mechanistic Studies on Glucagon and Cardiac Function

Glucagon receptor signaling increases cardiac contractility and heart rate through cyclic AMP-dependent pathways, effects described in detail in a 2021 review in Circulation [2]. This could benefit patients with acutely decompensated heart failure who need short-term inotropic support, but chronic glucagon receptor activation in a once-weekly subcutaneous peptide context has not been studied in heart failure patients. The clinical relevance of this mechanism for retatrutide specifically is speculative.

GRADE Evidence Rating Explained

The GRADE (Grading of Recommendations Assessment, Development and Evaluation) system rates evidence on four levels: High, Moderate, Low, and Very Low [10]. For retatrutide in heart failure specifically, the rating is Very Low because:

1. No direct randomized evidence exists with heart failure as the primary endpoint.
2. Available trial data (NCT04881760) were designed for weight reduction, not cardiac outcomes.
3. Extrapolation from GLP-1 class data introduces two levels of indirectness: the drug is different (triple vs. Single agonist) and the population studied differs.
4. Retatrutide has no completed Phase 3 trials in any indication.

A Very Low GRADE rating means the authors of a systematic review or guideline would have very little confidence that the true effect is close to the estimated effect. The GRADE Working Group defines this level as: "The true effect is probably markedly different from the estimated effect" [10].

For comparison, semaglutide 2.4 mg in HFpEF with obesity would receive a Moderate GRADE rating based on the single well-designed RCT (STEP-HFpEF) with consistent mechanistic plausibility.

Ongoing Research and What to Watch

Several trials include retatrutide arms or design features that may yield cardiac data within 12 to 24 months.

Phase 3 Obesity Trials With Cardiac Secondary Endpoints

Eli Lilly's TRIUMPH Phase 3 program for retatrutide in obesity includes pre-specified cardiovascular secondary endpoints: blood pressure, lipid panel, HbA1c, and inflammatory biomarkers [7]. If the Phase 3 data replicate the 22.8% weight loss seen in Phase 2 and show consistent blood pressure reductions, that will strengthen the biological rationale for heart failure trials, even without a dedicated heart failure arm.

The SURMOUNT-CVOT Design Question

For tirzepatide (a dual GIP/GLP-1 agonist and retatrutide's closest approved cousin), Eli Lilly is conducting SURMOUNT-CVOT, a dedicated cardiovascular outcomes trial [11]. A similar design for retatrutide has not been announced publicly. Clinicians should monitor ClinicalTrials.gov (NCT registry) for new retatrutide cardiac trial registrations.

HFrEF vs. HFpEF: Different Risk Profiles

HFpEF (ejection fraction ≥50%) driven by obesity is the subgroup most likely to benefit from retatrutide's weight reduction mechanism, mirroring the STEP-HFpEF population. HFrEF (ejection fraction <40%) is a different clinical scenario where the heart rate increase seen with glucagon receptor agonism (+2.6 bpm in NCT04881760) could be detrimental, particularly in patients on beta-blockers already maximized for rate control [5]. No safety data exist for retatrutide in HFrEF.

Approved Alternatives With Stronger Evidence

Clinicians managing heart failure patients who also have obesity or type 2 diabetes have several options with substantially stronger evidence.

SGLT2 Inhibitors: Standard of Care

Dapagliflozin (DAPA-HF, N=4,744) reduced the composite of worsening heart failure or cardiovascular death by 26% (HR 0.74, 95% CI 0.65 to 0.85, P<0.001) across both HFrEF and HFpEF subgroups [12]. Empagliflozin produced similar outcomes in EMPEROR-Reduced [13]. The 2022 AHA/ACC/HFSA Heart Failure Guideline gives SGLT2 inhibitors a Class I recommendation for HFrEF and a Class IIa recommendation for HFpEF [14].

Semaglutide in HFpEF With Obesity

Semaglutide 2.4 mg (Wegovy, FDA-approved for chronic weight management) is currently the only GLP-1 receptor agonist with direct randomized evidence in HFpEF [6]. The American Heart Association's 2023 scientific statement on obesity and heart failure acknowledged the STEP-HFpEF data as practice-informing, though formal guideline incorporation is still pending [15].

Combination Approaches

Many HFpEF patients with obesity benefit from combining an SGLT2 inhibitor (strong guideline support) with a GLP-1 receptor agonist (emerging evidence). Adding an investigational triple agonist to that combination before Phase 3 safety data exist is not supported by current evidence.

Safety Signals Relevant to Heart Failure Patients

Heart failure patients are a physiologically vulnerable population. Several retatrutide safety signals from Phase 2 deserve specific mention.

Gastrointestinal Adverse Events

In NCT04881760, nausea occurred in 47% of patients in the 12 mg arm vs. 14% placebo, and vomiting in 22% vs. 4% [5]. In patients with heart failure who are already fluid-sensitive, repeated vomiting can precipitate volume depletion, worsen renal function, and destabilize diuretic balance. This risk is not theoretical.

Heart Rate Increase

The +2.6 bpm mean heart rate increase with 12 mg retatrutide [5] is a class concern shared by GLP-1 agonists (liraglutide +2 to +3 bpm in LEADER [9]) but may be amplified by glucagon receptor co-agonism. In HFrEF patients with resting heart rates already above 70 bpm on maximized beta-blockade, even a modest additional heart rate increase could impair cardiac filling and worsen symptoms.

Renal Function

Acute kidney injury has been reported with GLP-1 receptor agonists in the setting of severe nausea and vomiting-induced volume depletion [1]. Heart failure patients on loop diuretics are at elevated baseline risk. No retatrutide-specific renal data from heart failure patients exist.

Unknown Long-Term Cardiovascular Safety

The LEADER trial for liraglutide required 9,340 patients and 3.8 years of follow-up to establish cardiovascular safety [9]. Retatrutide has been tested in fewer than 1,000 humans total across all trials to date, for no longer than 48 weeks, in populations selected to exclude significant cardiovascular comorbidities. The cardiovascular safety profile in heart failure patients is genuinely unknown.

Clinical Guidance: Who Should Not Receive Compounded Retatrutide for Heart Failure

Given the current evidence gap, the following patient profiles carry unacceptable risk-to-benefit ratios for off-label retatrutide use outside a clinical trial:

• HFrEF with EF <40% and resting heart rate >70 bpm on beta-blockade
• Decompensated heart failure requiring IV diuresis within the past 90 days
• Advanced CKD (eGFR <30 mL/min/1.73m²) due to absence of renal safety data
• History of GI dysmotility severe enough to compromise oral medication adherence
• Patients with HFpEF who are not obese (BMI <30), as the primary mechanism of hypothesized benefit (weight reduction) does not apply

Patients with HFpEF, BMI ≥35, who have failed or cannot access approved semaglutide, and who have been counseled about Very Low GRADE evidence, represent the narrowest plausible candidate profile. Even in that group, enrollment in a clinical trial is strongly preferred over off-label compounded use.