Retatrutide and Muscle Loss: What the Research Shows and How to Preserve Muscle (2026)

October 23, 2026

Does retatrutide cause muscle loss? The available evidence suggests that retatrutide-associated weight loss includes a reduction in lean mass, as occurs with other effective obesity treatments. However, the available studies do not establish how much actual skeletal muscle an individual will lose, whether the loss affects muscle function, or how much can be prevented through nutrition and exercise.

In a published Phase 2 body-composition substudy involving adults with type 2 diabetes, researchers observed substantial fat-mass reductions alongside reductions in lean mass. The results do not show that retatrutide uniquely damages muscle, but they also do not justify assuming that very large weight losses will preserve muscle automatically.

The practical priority is to pursue fat loss while preserving strength, physical function, adequate nutrition, and as much useful muscle as possible.

Evidence updated October 2026. This article is educational and is not a substitute for individualized medical advice.

Key findings at a glance

Lean mass can decrease: A Phase 2 DXA substudy documented reductions in both fat mass and lean mass during retatrutide treatment.
Lean mass is not synonymous with muscle: DXA measures body-composition compartments rather than isolated skeletal muscle.
The evidence remains limited: Only 103 participants completed both baseline and week-36 DXA scans in the published substudy.
Phase 3 weight loss is substantial: The published TRIUMPH-1 trial reported mean weight reductions of 17.6%, 23.7%, and 25.0% with the 4 mg, 9 mg, and 12 mg doses, respectively, under its treatment-regimen estimand. The primary publication did not establish how much of that weight loss was muscle.
Muscle preservation matters: Adequate protein, progressive resistance exercise, sufficient nutrition, and monitoring of strength and function are important during substantial weight loss.
Retatrutide remains investigational: It is not FDA-approved for routine clinical use as of October 2026.

1. What Is Retatrutide?

Retatrutide, also known as LY3437943, is an investigational once-weekly injectable medication developed by Eli Lilly. It activates three hormone receptors involved in metabolic regulation:

GIP receptor: Involved in glucose-dependent insulin secretion and metabolic regulation.
GLP-1 receptor: Involved in appetite regulation, glucose control, and slowing gastric emptying.
Glucagon receptor: Involved in regulating energy metabolism and glucose production.

Because it activates all three receptors, retatrutide is commonly described as a triple agonist. Clinical trials have demonstrated substantial average weight loss, making the quality of that weight loss an important research question.

For a person losing a large amount of weight, the goal is not simply a lower number on the scale. It is to reduce excess fat while maintaining muscle strength, mobility, nutritional status, and long-term health.

2. Does Retatrutide Cause Muscle Loss?

Some loss of lean mass has been documented during retatrutide treatment, but the evidence does not establish that retatrutide directly damages skeletal muscle.

When a person loses a substantial amount of weight, the body generally loses both fat mass and fat-free tissue. The balance depends on several factors, including the magnitude and speed of weight loss, baseline body composition, age, dietary protein, total energy intake, physical activity, and underlying health.

Retatrutide may contribute to this process indirectly by substantially reducing appetite and food intake. If a person eats too little protein, does not perform muscle-strengthening exercise, or experiences prolonged nausea or vomiting, preserving muscle can become more difficult.

These mechanisms are plausible explanations for why lean mass may fall during treatment. They should not be mistaken for proof that retatrutide has a specific muscle-toxic effect.

There is also an important distinction between three questions:

Does lean mass decrease? Yes, reductions have been observed in the published body-composition substudy.
Does retatrutide cause disproportionate muscle loss compared with other weight-loss treatments? The available substudy authors reported that the proportion of lean mass lost was similar to that seen with other obesity treatments.
Does retatrutide preserve muscle strength and function despite large weight loss? This requires more direct evidence. Weight-loss trials and questionnaires assessing physical function cannot, by themselves, establish that skeletal muscle has been preserved.

3. What Did the Retatrutide Body-Composition Study Find?

The most directly relevant published study is a 2025 body-composition substudy of a Phase 2 clinical trial in adults with type 2 diabetes. The results were published in The Lancet Diabetes & Endocrinology.

Researchers used dual-energy X-ray absorptiometry (DXA) to assess changes in body composition over 36 weeks. The prespecified primary endpoint was the percentage change in total fat mass.

Study design and limitations

189 participants were included in the substudy.
155 had a baseline DXA scan.
103 completed treatment and had both baseline and week-36 DXA scans.
Participants had type 2 diabetes and were enrolled in a Phase 2 trial, so the results cannot automatically be generalized to every person with obesity.

What happened to body fat?

The reported percentage reductions in total fat mass from baseline to week 36 were:

Treatment group	Mean reduction in total fat mass
Retatrutide 0.5 mg	4.9%
Retatrutide 4 mg, pooled groups	15.2%
Retatrutide 8 mg, pooled groups	26.1%
Retatrutide 12 mg	23.2%
Dulaglutide 1.5 mg	2.6%
Placebo	4.5%

These figures describe the change in total fat mass, not the percentage of total body weight lost. They also represent group averages rather than predictions for an individual.

What happened to lean mass?

The researchers also reported reductions in lean mass in exploratory analyses. Reductions reached approximately 6.5 kg in the higher-dose groups. Secondary analyses of the study data have estimated that lean mass accounted for roughly 38% of total weight loss in the higher-dose groups.

That figure needs careful interpretation. It is a study-specific estimate derived from a relatively small body-composition substudy, not a universal percentage applicable to every retatrutide user. It should not be read as meaning that 38% of the lost weight was necessarily skeletal muscle.

The study authors concluded that the proportion of weight loss attributable to lean mass was similar to that reported with other obesity treatments. This is somewhat reassuring, but it is not evidence that lean mass loss is absent or clinically unimportant.

Important limitation: The substudy was designed primarily to evaluate fat-mass changes, was relatively small, and did not directly isolate skeletal muscle or establish how much strength or muscle function changed in each participant.

Primary source: Effects of retatrutide on body composition in people with type 2 diabetes, The Lancet Diabetes & Endocrinology (2025). DOI: 10.1016/S2213-8587(25)00092-0.

4. What Do the Phase 3 Retatrutide Trials Tell Us About Muscle Loss?

The Phase 3 TRIUMPH-1 results provide stronger evidence about the magnitude of weight loss than the earlier Phase 2 trial. They do not, however, resolve the question of exactly how much skeletal muscle is lost.

In the trial published in the New England Journal of Medicine on September 29, 2026, 2,339 adults with obesity without diabetes were randomized to retatrutide or placebo for 80 weeks.

Treatment	Mean body-weight change at 80 weeks
Retatrutide 4 mg	−17.6%
Retatrutide 9 mg	−23.7%
Retatrutide 12 mg	−25.0%
Placebo	−3.9%

Source: TRIUMPH-1, New England Journal of Medicine, 2026. These are treatment-regimen estimand results; estimates differ from some analyses that address treatment discontinuation differently.

These findings demonstrate the potential for very large weight reductions. They do not mean that every participant lost the same percentage, nor do they demonstrate that all lost weight was fat.

The primary publication did not report direct body-composition measurements establishing what proportion of Phase 3 weight loss was skeletal muscle. Therefore, it would be premature to apply the Phase 2 lean-mass estimate directly to the larger Phase 3 weight reductions.

The most important unanswered questions include:

What proportion of weight loss is fat mass, other lean tissue, and skeletal muscle during long-term treatment?
Do changes differ by age, sex, baseline muscle mass, degree of obesity, dose, and rate of weight reduction?
How do muscle strength, power, mobility, and physical performance change over time?
Can structured nutrition and resistance exercise preserve more muscle without compromising treatment outcomes?

Primary source: Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. New England Journal of Medicine (2026). DOI: 10.1056/NEJMoa2604169.

5. Lean Mass Loss Is Not the Same as Muscle Loss

One of the most common mistakes in discussions of GLP-1 medicines and newer weight-loss drugs is treating the terms lean mass, fat-free mass, and muscle mass as interchangeable.

They are related, but they are not identical.

Term	What it means	Why it matters
Fat mass	The body's measured fat component.	A major target of obesity treatment when excess body fat contributes to disease risk.
Lean mass or lean soft tissue	Non-fat soft tissue, including muscle but also water, organs, and other tissues, depending on the measurement method.	A decline does not reveal exactly how much skeletal muscle has been lost.
Skeletal muscle mass	Muscles responsible for movement, posture, and much of voluntary physical activity.	Important for strength, mobility, metabolic health, and independence.
Muscle strength and function	The ability to produce force and carry out physical tasks.	Helps determine whether body-composition changes have meaningful functional consequences.

DXA is useful for estimating fat mass, lean soft tissue, and bone mineral content. However, it does not directly measure isolated skeletal muscle. MRI, certain CT assessments, strength testing, and functional tests answer different questions and may add useful information in selected clinical settings.

It is therefore possible to observe a decrease in DXA-measured lean mass without knowing exactly how much contractile muscle tissue was lost. Changes in body water and glycogen can also influence measured lean tissue during substantial weight loss.

This distinction does not mean lean-mass loss should be dismissed. It means that body-composition findings should be interpreted alongside strength, function, nutritional adequacy, and the person's overall health.

6. Who May Be More Vulnerable to Muscle Loss?

Not everyone losing weight on an incretin-based medication faces the same risk. Certain characteristics may increase the importance of muscle-preservation planning.

Older adults

Muscle mass and strength tend to decline with aging, especially in the presence of inactivity, inadequate nutrition, and chronic disease. An older adult who loses weight rapidly may have less physiological reserve than a younger person starting with greater muscle mass.

People with low muscle mass or poor physical function

A person can have obesity and still have low muscle mass or impaired muscle function, sometimes described as sarcopenic obesity. Body weight or BMI alone cannot establish whether someone has adequate muscle reserve.

People experiencing very low food intake

Strong appetite suppression can make it difficult to consume enough protein, energy, vitamins, and minerals. Skipping meals or eating very small portions without attention to nutrient density may worsen this problem.

People with persistent gastrointestinal symptoms

Ongoing nausea, vomiting, diarrhea, or early fullness may make it difficult to maintain sufficient fluid and nutrient intake. Persistent symptoms deserve clinical review rather than simply being accepted as part of weight loss.

People who do not perform resistance exercise

Weight loss without muscle-strengthening activity may provide less stimulus for retaining muscle. Walking and aerobic exercise are valuable for general health, but they do not completely replace progressive resistance training.

People with chronic disease or nutritional deficiencies

Some medical conditions, medications, and nutritional deficiencies affect muscle maintenance. Kidney disease can also change appropriate protein targets, so high-protein diets should not be prescribed without considering individual medical circumstances.

7. How to Preserve Muscle During Retatrutide Treatment

The following strategies are based on broader obesity-treatment evidence and clinical guidance. They are sensible measures for supporting muscle preservation, but they have not yet been proven in a dedicated randomized trial to prevent a specific percentage of muscle loss in people taking retatrutide.

Strategy 1: Prioritize adequate protein

Protein supplies the amino acids needed to maintain and repair muscle tissue. During substantial weight loss, an individual who eats much less than usual may unintentionally reduce protein intake at the same time that preserving lean tissue becomes more important.

The American Diabetes Association's 2025 obesity-care standards discuss a daily protein intake of approximately 1.2–1.6 grams per kilogram in the context of weight reduction, while emphasizing personalization. This is not a universal prescription for every retatrutide user.

The correct target depends on factors such as body size, age, baseline nutritional status, kidney function, activity level, total energy intake, and the weight used for the calculation. Using actual body weight in someone with substantial obesity can produce a target that needs adjustment. A clinician or registered dietitian can help establish a suitable goal.

Examples of protein-containing foods include:

Eggs, fish, poultry, and lean meats.
Milk, yogurt, Greek yogurt, cottage cheese, and other dairy foods.
Soy foods such as tofu, tempeh, and edamame.
Beans, lentils, chickpeas, and other legumes.
Protein-fortified foods or protein drinks when ordinary meals are insufficient.

Rather than trying to consume most of the day's protein in one sitting, many people find it easier to include a meaningful protein source in each main meal. Smaller, more frequent meals may be useful when appetite is reduced.

Important: More protein is not automatically better. People with chronic kidney disease or other conditions requiring dietary modification should establish their protein target with their healthcare team.

Strategy 2: Perform progressive resistance training

Resistance training gives muscles a reason to retain strength and tissue during a calorie deficit. It may involve free weights, resistance machines, bands, or appropriately selected bodyweight exercises.

For adults who are medically able to exercise, a practical starting framework is:

Frequency: Begin with two sessions per week, progressing toward two or three sessions as tolerated.
Coverage: Train the major muscle groups, including the legs, hips, back, chest, shoulders, and arms.
Progression: Increase resistance, repetitions, or total training volume gradually as strength and technique improve.
Recovery: Allow adequate recovery between challenging sessions and adjust the plan when fatigue or illness interferes with training.

Beginners do not need to lift very heavy weights immediately. Consistent, appropriately challenging exercise performed with suitable technique is more useful than an aggressive programme that cannot be sustained.

Older adults, people with joint pain, those with cardiovascular disease, and people with significant mobility limitations may need a supervised or adapted exercise programme.

Strategy 3: Do not rely on protein alone

Protein supports muscle maintenance, but a high-protein diet alone cannot guarantee muscle preservation. Resistance exercise, adequate energy intake, recovery, and consistency also matter.

A person who substantially reduces food intake may struggle to meet overall nutritional needs even when protein intake appears adequate. Very restrictive dieting can also make it more difficult to sustain exercise and recover between sessions.

During treatment, prioritize nutrient-dense meals that include protein, vegetables, fruit, suitable sources of carbohydrate, and healthy fats. The appropriate amount of food depends on individual needs and treatment goals; adequate nutrition does not require abandoning the objective of reducing excess body fat.

Strategy 4: Manage nausea and early fullness before nutrition deteriorates

Retatrutide trial participants commonly reported gastrointestinal adverse effects, including nausea, diarrhea, constipation, and vomiting. These symptoms can make it harder to eat, drink, and maintain a balanced diet.

Practical measures that may help include:

Eating smaller meals and stopping before uncomfortable fullness.
Choosing foods that are better tolerated instead of repeatedly forcing foods that trigger symptoms.
Including protein in smaller meals or snacks when full-sized meals are difficult.
Maintaining fluid intake in accordance with individual medical advice.
Contacting the treating clinician if symptoms persist, nutritional intake falls substantially, or the ability to exercise deteriorates.

Do not independently increase, reduce, or change the dosing schedule of an investigational medication in an attempt to manage muscle loss. Any treatment adjustments must be handled by the clinical trial team or treating clinician, as appropriate.

Strategy 5: Maintain aerobic activity and daily movement

Walking, cycling, swimming, and other suitable aerobic activities support cardiovascular health and physical capacity. Daily movement can also help prevent the inactivity that sometimes accompanies reduced energy intake or fatigue.

Aerobic exercise complements, rather than replaces, resistance training. The right programme should be tailored to current fitness, physical limitations, recovery, and personal preferences.

Strategy 6: Pay attention to sleep and recovery

Sleep and recovery are important for exercise performance, appetite regulation, and the ability to maintain regular physical activity. Persistent fatigue should not automatically be attributed to the medication; inadequate nutrition, dehydration, poor sleep, and unrelated medical problems may also contribute.

Where possible, establish a sustainable routine rather than combining aggressive calorie restriction with a sudden, high-volume exercise programme.

8. Does Taking a Protein Supplement Prevent Retatrutide-Related Muscle Loss?

Protein supplements may help people who struggle to obtain sufficient protein from food. They do not guarantee that muscle will be preserved.

The decision to use a protein powder or ready-to-drink product should be based on actual dietary intake, tolerance, nutritional requirements, cost, and individual health considerations.

A supplement is best viewed as a convenient source of protein when needed, not a substitute for an adequate diet and appropriate resistance exercise.

There is currently no established retatrutide-specific supplement protocol proven to eliminate lean-mass loss. Claims that a particular amino acid, peptide, vitamin, or commercial product completely prevents muscle loss should be treated skeptically unless supported by suitable clinical evidence.

9. How Should Muscle Preservation Be Monitored?

The number on the scale is an incomplete measure of treatment quality. Monitoring should consider body composition when appropriate, but also strength, physical function, nutrition, and how well the person is managing daily activities.

Monitoring method	What it helps assess	Main limitation
Body weight and waist circumference	Overall weight trajectory and changes in central body size.	Cannot determine how much weight comes from fat, muscle, or other tissue.
Dietary and protein-intake assessment	Whether food intake is sufficient and nutritionally balanced.	Reported intake may be incomplete and does not directly measure muscle.
Grip strength or chair-stand test	Selected measures of strength and physical function.	Performance can be affected by pain, fatigue, technique, and other conditions.
DXA body-composition assessment	Estimates of fat mass, lean soft tissue, and bone mineral content.	Does not directly isolate skeletal muscle; results may be affected by hydration and measurement conditions.
Clinical nutrition and medical review	Symptoms, nutritional risk, medication tolerance, and possible causes of weakness.	The assessment must be individualized; there is no single test that answers every question.

Potential warning signs include progressive weakness, recurrent falls, decreasing ability to rise from a chair or climb stairs, persistently poor food intake, and difficulty maintaining ordinary activities.

These symptoms do not automatically prove muscle loss, but they warrant clinical assessment. Persistent vomiting, inability to keep fluids down, fainting, or severe or persistent abdominal pain requires prompt medical evaluation.

10. Retatrutide Versus Semaglutide and Tirzepatide: Is Muscle Loss Different?

It is tempting to rank weight-loss medications by the amount of muscle they preserve. The available data do not yet support a reliable ranking of retatrutide, semaglutide, and tirzepatide for muscle preservation.

Published body-composition studies differ in their populations, duration, degree of weight loss, measurement methods, and analysis. A study enrolling participants with type 2 diabetes cannot necessarily be compared directly with a study enrolling people with obesity without diabetes.

Medicine	What the evidence tells us	Important limitation
Retatrutide	A Phase 2 DXA substudy showed reductions in fat mass and lean mass.	The detailed body-composition evidence remains limited and does not establish a Phase 3 skeletal-muscle effect.
Semaglutide	Body-composition analyses have documented reductions in fat mass and lean mass during weight loss.	Results vary across trials and populations, and lean mass is not synonymous with muscle.
Tirzepatide	Body-composition analyses have also documented loss of fat mass and lean mass.	Findings cannot be compared with retatrutide without accounting for differences in study design and total weight loss.

A systematic review and network meta-analysis published in 2025 found that GLP-1 receptor agonists and related therapies reduced weight, fat mass, and lean mass in the trials analyzed. The authors estimated that lean mass accounted for approximately one-quarter of total weight loss across the included studies, although individual study results varied.

The retatrutide substudy's higher estimated proportion should therefore be interpreted in its own study context, rather than used to conclude that retatrutide is necessarily worse than another medicine.

Relevant research: Effect of GLP-1 receptor agonists and co-agonists on body composition: systematic review and network meta-analysis (2025).

11. Retatrutide Safety and Regulatory Status

As of October 23, 2026, retatrutide remains an investigational medicine and is not FDA-approved for routine clinical use. Eli Lilly has stated that it plans to submit a Biologics License Application to the FDA in the first quarter of 2027.

In Phase 3 trials, commonly reported adverse effects included gastrointestinal symptoms such as nausea, diarrhea, constipation, and vomiting. Trial results also require ongoing assessment of less common adverse effects and longer-term safety.

Retatrutide should not be treated as an established, approved weight-loss prescription simply because encouraging clinical-trial results have been published.

Products sold online as research retatrutide or for self-injection outside authorized clinical research may have uncertain identity, purity, concentration, sterility, and safety. Buying a product marketed under that name does not establish that it is equivalent to the investigational medicine used in clinical trials.

Clinical-trial information: TRIUMPH-1, ClinicalTrials.gov.

12. What Healthcare Professionals Should Discuss With Patients

Muscle preservation should be incorporated into obesity treatment from the beginning, rather than addressed only after substantial weight loss has occurred.

A practical consultation can cover the following areas:

Baseline risk: Assess age, prior weight changes, muscle-strength concerns, mobility, nutritional status, comorbidities, and current activity level.
Nutrition: Review dietary intake and protein adequacy; identify food intolerance, restrictive eating, or symptoms that interfere with nutrition.
Exercise: Establish a realistic progressive resistance-training plan, with modifications where pain, frailty, or other medical conditions are present.
Monitoring: Track functional changes and clinical symptoms in addition to weight and waist circumference. Use body-composition testing when it is clinically useful.
Treatment tolerability: Review persistent gastrointestinal symptoms, hydration, food intake, and any decline in the ability to maintain daily activities.
Shared decision-making: Evaluate overall benefits, risks, treatment goals, preferences, and alternatives rather than focusing exclusively on the largest possible weight reduction.

The American Diabetes Association's obesity-care standards recommend adequate protein intake and muscle-strengthening activities to help minimize muscle loss during weight reduction. These recommendations provide a useful foundation for care while retatrutide-specific evidence continues to develop.

Guideline: Pharmacologic Treatment of Obesity in Adults: Standards of Care in Overweight and Obesity.

13. What Research Is Still Needed?

The next step in the evidence base should be more than another demonstration that retatrutide reduces body weight. Better studies need to establish whether that weight reduction preserves muscle and physical function in the long term.

Useful research priorities include:

Large, prospective body-composition substudies embedded in Phase 3 trials.
Standardized measurements of skeletal muscle, fat mass, and lean soft tissue at baseline and follow-up.
Objective muscle-function outcomes, such as grip strength, chair-stand performance, gait speed, or other validated functional assessments.
Analyses stratified by age, sex, diabetes status, baseline muscle mass, and magnitude of weight loss.
Controlled studies of protein intake and progressive resistance training during retatrutide-associated weight reduction.
Longer-term follow-up examining recovery, maintenance of strength, weight regain, and the balance of benefits and harms.

Such studies could clarify whether the proportion of lean mass loss changes with the magnitude of weight reduction and which interventions offer the greatest benefit to patients at higher risk of muscle impairment.

Frequently Asked Questions

Does retatrutide cause muscle loss?

Lean-mass reductions have been observed in a Phase 2 DXA substudy of retatrutide. However, lean mass includes more than skeletal muscle, and the available evidence does not establish that retatrutide directly damages muscle or predict the exact amount of muscle an individual may lose.

What percentage of weight lost on retatrutide is muscle?

No reliable universal percentage is established for skeletal muscle. Secondary analyses of the Phase 2 body-composition data have estimated that roughly 38% of weight loss in higher-dose groups was lean mass. That estimate is study-specific, and lean mass is not equivalent to muscle mass.

How much lean mass can be lost on retatrutide?

Exploratory analyses of the published 36-week Phase 2 body-composition substudy reported reductions in lean mass of up to approximately 6.5 kg. This finding should not be used to predict an individual's outcome, particularly because the substudy was relatively small and involved adults with type 2 diabetes.

Is retatrutide worse for muscle loss than semaglutide or tirzepatide?

There is not enough directly comparable evidence to rank these medicines reliably by muscle preservation. Studies differ in participants, duration, magnitude of weight loss, and measurement techniques. The retatrutide body-composition substudy authors concluded that the proportion of lean mass loss was similar to other obesity treatments.

Can protein and weight training prevent muscle loss on retatrutide?

Adequate protein and resistance training are evidence-based components of muscle-preservation strategies during weight loss. They may reduce the risk of excessive muscle loss, but there is no retatrutide-specific trial evidence proving that they eliminate it completely.

How much protein should someone consume while losing weight?

The appropriate target depends on body size, nutritional status, age, activity, and kidney function. Obesity-care guidance discusses targets around 1.2–1.6 g/kg/day in relevant weight-loss settings, but the calculation should be individualized, particularly in people with substantial obesity or chronic kidney disease.

Does losing lean mass always mean losing strength?

No. Changes in DXA-measured lean mass do not directly quantify changes in strength. Strength tests and physical-function assessments provide complementary information and can help determine whether body-composition changes are associated with meaningful functional decline.

Is retatrutide approved for weight loss?

As of October 23, 2026, retatrutide remains investigational and is not FDA-approved for routine clinical use. Eli Lilly has stated that it plans to submit its application to the FDA in the first quarter of 2027.

Conclusion: Focus on the Quality of Weight Loss, Not Just the Number on the Scale

Retatrutide has demonstrated substantial weight-loss efficacy, but the available evidence confirms that lean mass can also decline during treatment. The direct body-composition evidence remains limited, and a reduction in lean mass does not tell us precisely how much skeletal muscle has been lost or whether strength has deteriorated.

The appropriate response is neither to dismiss the concern nor to assume that retatrutide inevitably causes clinically significant muscle damage. Instead, muscle preservation should be treated as a measurable part of responsible weight management.

For people pursuing substantial weight loss, the priorities remain consistent: adequate nutrition and protein, progressive resistance exercise, management of treatment-related symptoms, and monitoring of strength and daily function. As retatrutide research advances, larger studies measuring body composition and muscle function will be needed to establish how well these strategies work specifically during retatrutide treatment.

OneDayMD perspective: Successful obesity treatment should be judged not only by how much weight a person loses, but also by how well that person maintains strength, mobility, nutritional health, and long-term physical function.

References and Further Reading

Jastreboff AM, et al. Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. New England Journal of Medicine. 2023;389:514–526. https://doi.org/10.1056/NEJMoa2301972
Coskun T, et al. Effects 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. 2025;13(8):674–684. https://doi.org/10.1016/S2213-8587(25)00092-0
Jastreboff AM, et al. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. New England Journal of Medicine. Published September 29, 2026. https://doi.org/10.1056/NEJMoa2604169
Effect of glucagon-like peptide-1 receptor agonists and co-agonists on body composition: systematic review and network meta-analysis. PubMed record
American Diabetes Association. Pharmacologic Treatment of Obesity in Adults: Standards of Care in Overweight and Obesity. Clinical practice guidance
Eli Lilly and Company. Retatrutide Phase 3 clinical-trial and regulatory-development updates. Official investor and clinical-development announcements

Editorial and medical disclaimer: OneDayMD provides educational health information and does not replace individualized medical advice, diagnosis, or treatment. Clinical-trial findings may not apply to every individual. Retatrutide remains investigational as of the date of this article; treatment decisions and participation in clinical research should be discussed with qualified healthcare professionals.