Key takeaways

GLP-1 receptor agonists like semaglutide and tirzepatide work by mimicking a hormone your body already releases after eating — reducing appetite, slowing gastric emptying, and changing how the brain processes food cues. The clinical evidence is substantial; the regulatory environment around compounded versions changed materially in 2025–2026. Side effects are manageable but real, muscle loss is the most under-addressed risk, and what happens after you stop matters as much as how well it works while you are on it. Here is what the evidence actually shows.

GLP-1 receptor agonists became one of the most-prescribed medication classes in the United States by 2025–2026 — at the peak, prescription data from sources including IQVIA put them at roughly 8% of all new prescriptions in some months of early 2026. That is not a wellness trend. That is a medical shift.

For many people, these medications have done what decades of dieting could not. But the clinical picture is more nuanced than the before-and-after photos suggest. Muscle loss is real. The side effect profile demands management. The regulatory landscape around compounded versions changed materially in 2025–2026, and what was true a year ago is no longer the same as what is true now.

Here is what the evidence actually shows — and what to look for in any program that prescribes these medications.

How GLP-1 Medications Actually Work

GLP-1 stands for glucagon-like peptide-1. It is a natural hormone your gut releases after eating. It does several things at once: it tells the pancreas to release insulin (which is why GLP-1 receptor agonists were originally developed for type 2 diabetes), it slows the rate at which food leaves the stomach (which extends fullness after a meal), and it acts on receptors in the brain that regulate hunger (which reduces the constant background drive to eat).

Semaglutide is a synthetic version that is about 94% identical to native GLP-1 but engineered to last in the body for a week instead of minutes. Tirzepatide is a dual agonist — it activates both the GLP-1 receptor and a second receptor called GIP, which contributes additional insulin-sensitizing and appetite-regulating effects.

The clinical experience that most patients describe is not that they feel less hungry in a willpower sense. They feel like the food noise in their head — the constant background presence of thinking about what to eat next — quiets down. For people who have spent decades fighting that signal, the change can feel like a different relationship with food.

Semaglutide vs. Tirzepatide — What the Evidence Shows

Both medications are highly effective. The head-to-head data — particularly the 2025 SURMOUNT-5 trial — showed tirzepatide producing somewhat greater average weight reduction than semaglutide over 72 weeks (approximately 20% vs. 14% mean body weight reduction). For most people, both produce meaningful results; for some, tirzepatide produces more.

Practical considerations beyond efficacy:

Side effect profile: very similar between the two, though some patients tolerate one better than the other for reasons that are not fully predictable.

Cost and availability: depending on insurance coverage, the practical access to one vs. the other can vary substantially.

Cardiovascular evidence: semaglutide has the larger trial database for cardiovascular outcomes, including the SELECT trial, which showed a 20% reduction in major adverse cardiovascular events (MACE) in semaglutide-treated patients with overweight or obesity and established cardiovascular disease, without diabetes. Tirzepatide outcomes trials are ongoing.

There is no universally correct first choice. The right starting medication depends on your individual picture, your insurance coverage, and how you tolerate the first few weeks. A reasonable program should be able to switch if needed.

The Compounding Landscape in 2026

This is the section where context matters most. The regulatory environment is meaningfully different now than it was 18 months ago.

From 2022 through early 2025, compounded semaglutide and tirzepatide were widely available through 503A compounding pharmacies under an FDA shortage designation. The shortage designation allowed pharmacies to prepare these medications because patients could not reliably get the brand-name versions.

Both shortages have been resolved — tirzepatide in late 2024, semaglutide in February 2025. The grace periods for compounding under shortage have ended. In March 2026, the FDA issued warning letters to 30 telehealth companies for marketing practices that implied compounded versions were equivalent to FDA-approved brand-name medications.

Compounding remains legal in specific circumstances — for example, when a patient has a documented allergy to an inactive ingredient in the commercial product, or requires a dose that is not commercially available. That is called the medical-necessity pathway, and it is the legitimate framework under which compounded GLP-1 medications can still be prescribed.

What this means in practice: if a clinic is advertising compounded GLP-1 medications as equivalent alternatives to the brand-name products, or as a way to access the same medicine for less money, that is the kind of language the FDA has explicitly flagged. A clinically defensible program treats compounded medications as one option that requires individualized medical justification — not as the default.

Side Effects — The Honest Guide

GI Symptoms

Nausea, occasional vomiting, constipation, and diarrhea are the most common side effects. They are typically dose-related and most pronounced during the first few weeks after a dose increase. The majority of people see GI symptoms ease meaningfully by the third or fourth week on a given dose.

Strategies that help: starting at the lowest approved dose, escalating slowly, eating smaller meals, avoiding high-fat foods in the first day or two after each dose, staying hydrated.

Gastroparesis Concerns

GLP-1 medications slow gastric emptying as part of their mechanism. In a small subset of patients, this becomes clinically problematic. If symptoms include persistent vomiting, severe upper abdominal pain, or an inability to keep food down, this needs to be evaluated promptly — it is not normal nausea and should not be managed at home.

Thyroid Concerns

These medications carry a boxed warning related to thyroid C-cell tumors observed in rodent studies. Post-marketing surveillance over more than a decade of GLP-1 use in humans has not detected a signal of medullary thyroid carcinoma risk. An absolute contraindication is a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 — these are rare but important to ask about before starting.

Other Label Warnings Worth Knowing

Three additional items round out the standard informed-consent conversation:

Acute pancreatitis — uncommon but real. New, severe, persistent abdominal pain that radiates to the back warrants immediate evaluation and stopping the medication.

Pregnancy — GLP-1 medications are not recommended in pregnancy and are typically stopped well before planned conception. Effective contraception during use is part of the conversation for women of reproductive age.

Suicidal ideation — the FDA and European Medicines Agency have both reviewed reports of suicidal ideation in GLP-1 users; no causal link has been established to date, but new or worsening mood symptoms should be raised with your physician promptly.

Facial Volume Loss ('Ozempic Face')

Significant weight loss in a short period reduces subcutaneous fat including in the face. This is not a unique side effect of GLP-1 medications — it would happen with any rapid weight loss — but the rate of loss with GLP-1s makes it more visible. Slower weight loss, adequate protein, and resistance training all help moderate the cosmetic effect.

Muscle Loss — The Most Underdiscussed Risk

Estimates of how much GLP-1-induced weight loss comes from lean tissue range from approximately 25% to 40% across studies, with the higher end seen in faster weight loss and lower protein intake conditions. Muscle is metabolically active tissue that drives baseline calorie burn, supports glucose handling, and protects against fall and frailty risk in the long term. Losing it makes weight regain easier and metabolic health harder.

The published evidence and clinical experience agree on what helps preserve lean mass:

Adequate protein intake — for most adults losing weight on a GLP-1, that means approximately 1.2 to 1.6 grams of protein per kilogram of body weight per day. This is materially higher than typical Western intake.

Resistance training at least twice weekly, ideally three. Walking is good for general health but does not preserve muscle the way resistance training does.

Slower, sustainable weight loss. Aggressively pushing the rate of loss tends to come at the cost of more lean tissue.

A GLP-1 program that does not address muscle preservation — protein targets, training, and monitoring — is leaving meaningful clinical value on the table.

What Happens When You Stop

The published data is honest about this: most people who stop GLP-1 medications regain a substantial portion of the weight they lost over the following 12–18 months. The signaling that the medication provided — quieter food noise, slower gastric emptying, sustained fullness — goes away when the medication does.

This is increasingly being framed by endocrinologists as a feature, not a bug. Obesity is increasingly understood as a chronic condition with metabolic and hormonal drivers, not a failure of willpower. Maintenance therapy — staying on the medication at a lower dose for the long term — is the model many clinicians use, and it is the model the trial data supports.

For people who want to come off the medication, the transition is possible but it requires a plan: tapering rather than stopping abruptly, building the lifestyle infrastructure (protein, training, sleep, sustainable food choices) during the period of medication-supported weight loss, and being prepared for the food noise to return.

How Leader Health Approaches This

At Leader Health, GLP-1 therapy is a physician-led program — not a one-click prescription. Your intake includes a metabolic assessment, baseline lab work, a protein and training plan designed around preserving lean mass, and a real conversation about the long-term picture, including what maintenance therapy looks like if it is the right call for you.

If you have been considering a GLP-1 medication and want a program that takes the medication seriously as medicine — not as a transaction — this is the right starting point.

References

1. Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5). N Engl J Med. 2025. PMID: 40353578.

2. Wadden TA, et al. Tirzepatide after Intensive Lifestyle Intervention in Adults with Overweight or Obesity: The SURMOUNT-3 Phase 3 Trial. Nat Med. 2023.

3. Lincoff AM, et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT). N Engl J Med. 2023.

4. Jastreboff AM, et al. Tirzepatide once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022.

5. FDA. Press Release: FDA Warns 30 Telehealth Companies Against Illegal Marketing of Compounded GLP-1s. March 3, 2026. fda.gov/news-events/press-announcements/fda-warns-30-telehealth-companies-against-illegal-marketing-compounded-glp-1s.

6. FDA. Statement on Compounding Following Resolution of GLP-1 Supply. April 2026.

7. UCSF. Are the New Weight Loss Drugs Too Good to Be True? June 2024.

8. IQVIA Institute. The Use of Medicines in the U.S. — GLP-1 prescription volume data. 2025-2026.