The GLP-1 Miracle
What We Don’t Know Yet and Why That Matters
In December 1950, the Nobel Committee in Stockholm awarded its Prize to Philip Hench and Edward Kendall, the men who gave Mrs. G. her life back two years earlier. The press erupted, the word miracle was used without qualification, without caveat, without the measured language that medicine is supposed to require.
Then, years later, the darker picture began to emerge. Patients on chronic cortisone therapy were developing consequences the initial trials had not predicted.
In his Nobel lecture delivered in Stockholm that same December, Philip Hench stated explicitly that cortisone appeared to act not by resolving the causes of disease but by suppressing its manifestations. However the cultural momentum of the miracle had already moved beyond any individual’s ability to slow it down. We may be living through a version of this moment right now.
A Position Statement, Before the Concerns
GLP-1 receptor agonists are genuine therapeutic breakthroughs. The cardiovascular, hepatic, and renal outcome data reviewed in Part 1 of this series are among the most compelling trial results metabolic medicine has produced. For patients with significant obesity and metabolic comorbidities, for patients with type 2 diabetes, for patients with established cardiovascular disease meeting the criteria established in the SELECT trial, these drugs when used appropriately are as close to a miracle as medicine can deliver. I am unequivocally in favor of their use in patients with legitimate clinical indications.
What We Know We Don’t Know, The Long-Term Safety Gap
GLP-1 receptor agonists have been in widespread clinical use for obesity management for approximately four years. The longest cardiovascular outcomes trials run to roughly five years of follow-up, conducted in carefully selected patient populations. The broad population now receiving these drugs, including younger adults without significant metabolic comorbidity, patients using them primarily for cosmetic weight loss, or patients with health conditions and medication combinations the clinical trials did not study, has no decade-plus safety data to draw on.
Rodent carcinogenicity studies showed statistically significant increases in thyroid C-cell adenomas at all dose levels, generating an FDA black box warning on every semaglutide product label today. Current human data are more reassuring: a large multisite international cohort study across six countries involving 98,147 GLP-1 receptor agonist users, published by Baxter and colleagues in Thyroid in 2025, found no increased risk of thyroid cancer compared to users of alternative diabetes medications over follow-up of 1.8 to 3.0 years. A 2025 propensity-matched analysis by Pollack and Stokar in Diabetes/Metabolism Research and Reviews, covering 89,646 patients with approximately one decade of follow-up, similarly found no increased thyroid cancer risk.
The authors of both studies explicitly stated that their follow-up periods are insufficient to evaluate long-term risk, and that the study populations with type 2 diabetes may not represent the growing non-diabetic cohort now using these drugs. The American Thyroid Association’s January 2025 commentary characterized the reassuring findings appropriately: promising, incomplete, and requiring longer observation. Medullary thyroid carcinoma is rare and carries long latency periods that may require decades of follow-up to fully characterize.
The Muscle Problem Few Consider
What the trials show. Clinical trial data consistently demonstrate that between 25% and 45% of weight lost on GLP-1 therapy comes from lean mass rather than fat alone. In the STEP-1 trial of semaglutide, lean mass loss accounted for approximately 40–45% of total weight lost. In SURMOUNT-1 with tirzepatide, approximately 26%. A 2025 meta-analysis of 22 randomized controlled trials by Karakasis and colleagues in Metabolism confirmed lean mass loss comprising roughly 25% of total weight loss across the drug class, with Neeland and colleagues in Diabetes, Obesity and Metabolism in 2024 reviewing the mitigation strategies in detail. The proportion of lean mass loss is modifiable with structured resistance exercise three to five days per week and adequate dietary protein intake, Case series published in PMC in 2025 demonstrate that patients can maintain or even gain lean mass while losing significant fat under supervised conditions.
Why muscle mass is not merely cosmetic. Skeletal muscle accounts for approximately 70–80% of whole-body insulin-stimulated glucose disposal. Less widely appreciated is what Richter and Hargreaves documented in their foundational 2013 review in Physiological Reviews: muscle contraction stimulates glucose uptake through a pathway that is independent of insulin, via GLUT4 transporter translocation driven by the contraction itself, mediated through AMPK activation rather than insulin receptor signaling.
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In plain language: when you exercise, your muscles pull glucose out of the bloodstream through a door that does not require insulin to open. For a patient with insulin resistance, exercising muscle is one of the few remaining mechanisms through which glucose can be cleared efficiently. When you reduce the mass of the tissue capable of performing that function, you reduce the metabolic benefit of exercise itself. While exercise remains beneficial, its capacity to compensate for insulin resistance has been diminished.
The functional dimension. Muscle mass is also the biological substrate of physical independence: the capacity to climb stairs, rise from a chair without assistance, carry groceries, maintain balance, recover from illness. Sarcopenia (muscle mass loss) in older adults is one of the leading drivers of functional independence loss and increased mortality risk.
The age dimension. The biology of muscle recovery becomes more difficult with age. This is a well-characterized physiological phenomenon called anabolic resistance, defined as the age-related blunting of the muscle protein synthetic response to both protein intake and resistance exercise. Breen and Phillips, publishing in PubMed in 2013, established the mechanistic basis; Aragon, Tipton, and Schoenfeld in Nutrition Reviews in 2023 reviewed the question of whether this resistance is inevitable or preventable; and a 2023 review in Nutrients/PMC examined the specific interventions capable of counteracting it. Aging muscle is less sensitive to lower doses of amino acids and responds less robustly to resistance exercise than younger muscle.
You Don’t Return to Where You Started
The STEP-4 trial established clearly that stopping semaglutide leads to substantial weight regain in most patients within months (Wilding et al., NEJM, 2022). Budini and colleagues’ 2025 systematic review and meta-regression on medRxiv confirmed the trajectory. What is less discussed is the likely composition of that regained weight.
Weight lost on GLP-1 therapy includes a meaningful proportion of lean mass. Weight regained after discontinuation follows the well-established pattern of caloric restriction recovery: muscle is preferentially catabolized during restriction, and fat is preferentially restored during repletion. This physiological asymmetry, compounded by anabolic resistance in older patients, means a patient who stops the drug and regains their weight has not simply returned to their starting point, they may have more fat, less muscle, and a reduced capacity to recover the lean tissue that was lost. Shah and colleagues’ 2026 analysis in Diabetes, Obesity and Metabolism addresses the clinical management implications of this trajectory. The body composition data on the regain phase specifically remains limited, this is a physiologically sound inference from established biology, not a directly measured outcome in GLP-1 discontinuation studies.
The patient who discontinues the drug without the muscle-preservation infrastructure in place may be in a worse metabolic position than before they started.
An Emerging Adverse Effect Worth Noting
Post-marketing surveillance has generated reports of delayed gastric emptying severe enough to be classified as gastroparesis (partial or complete loss of gastrointestinal motility) in some patients on GLP-1 therapy. The FDA label for semaglutide states explicitly that it is not recommended in patients with severe gastroparesis. Whether this represents a true drug-induced complication or reflects the detection of pre-existing gastrointestinal dysmotility in a population already at elevated risk remains an actively investigated question; direct causality has not been established.
The Commercial Prescribing Problem
The concern here is with a specific commercial model: an online platform that profits from selling a drug, conducts a brief assessment without physical examination, laboratory evaluation, or assessment of relevant comorbidities, prescribes the drug without establishing baseline body composition or nutritional status, provides little or no structured dietary or resistance exercise counseling, and offers minimal ongoing clinical monitoring.
The evidence for concern is documented and specific. A survey of 2,000 primary care physicians conducted by Omada Health and reported in the Medical Liability Monitor in March 2025 found that 67% believe GLP-1 prescriptions by third-party telehealth providers pose a significant patient safety risk. 77% of those same physicians reported conducting a thorough physical evaluation before prescribing, assessing for comorbidities including diabetes, cardiovascular disease, and hypertension. More than half require patients non-pharmacological interventions before considering a prescription. Published literature reviewed in a 2025 PMC analysis of access to GLP-1 medications, documents that many online platforms ship compounded GLP-1 drugs after a questionnaire only, with no laboratory work, lifestyle counseling, or in-person physician visit required. As reported by STAT News in March 2026, the FDA has issued warning letters to more than 70 telehealth companies regarding their marketing of compounded GLP-1 medications. State medical boards have taken disciplinary action against prescribers operating through platforms that failed to meet minimum standards for establishing a legitimate physician-patient relationship. Golovaty and Hagan, writing in the New England Journal of Medicine in February 2024, identified the structural tensions between direct-to-consumer prescribing models and responsible clinical practice.
The patients most at risk by this model are those the drug is least likely to serve appropriately: patients without significant metabolic disease seeking a cosmetic result, who will not receive the dietary and exercise guidance that protects lean mass, and who will discontinue when the cost becomes unsustainable or the side effects intolerable.
What Responsible Use Actually Looks Like
These drugs, used correctly, are remarkable. Used correctly means: clear clinical indications, comprehensive baseline assessment including laboratory evaluation and body composition, structured dietary counseling with specific attention to protein intake adequate to protect lean mass during weight loss, resistance exercise as a component of the treatment plan, regular monitoring of weight, body composition, and metabolic parameters throughout treatment. It also means an honest conversation with every patient about the lifelong nature of this commitment before prescribing, not after six months when side effects or financial limitations threaten compliance.
And so I leave you dear reader, with this caution:
“Those who cannot remember the past are condemned to repeat it.” — George Santayana, The Life of Reason, 1905
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