Peptides and Weight Loss: Semaglutide and Tirzepatide
How semaglutide and tirzepatide are changing the treatment of obesity
Semaglutide and tirzepatide have expanded the possibilities for treating obesity. By acting on signals that regulate appetite and metabolism, they allow many people to achieve meaningful weight loss with medical supervision. Their arrival also invites us to revisit an idea that dominated the conversation about the body for years: that losing weight depends solely on willpower.
Obesity is a complex, chronic disease. Addressing it requires understanding each person's health and circumstances. In December 2025, the World Health Organization published conditional recommendations on the long-term use of these therapies in adults with obesity, as part of comprehensive care. Their conditional nature acknowledges both the benefits and the uncertainties about very long-term use, costs, and access. [1]
To understand what is changing, it helps to know what these medications are, what results they have shown, and what role nutrition and training play. Rigorous information makes it possible to weigh their potential without turning it into a promise of guaranteed transformation.
What peptides are and how they act in the body
Peptides are chains of amino acids, the same units that make up proteins. Some take part in communication between organs and act as hormonal signals. Medicine can develop molecules that mimic or modify certain signals to achieve a therapeutic effect.
Semaglutide and tirzepatide belong to this field. They are peptide-based medications that act on receptors related to incretins, hormones involved in the body's response to food. Their effects include changes in glucose control and food intake. [2, 3]
The term "peptide," on its own, doesn't tell you whether a product is effective, safe, or appropriate for a given person. The results of one studied molecule can't automatically be applied to other substances sold under the same label. What matters is the active ingredient, the formulation, and the evidence specific to that product.
Semaglutide and tirzepatide, clearly explained
Semaglutide activates the GLP-1 receptor. It promotes insulin release when glucose is elevated and is involved in mechanisms that regulate appetite. It can help you feel full and reduce the amount of food you eat. It also slows stomach emptying, although its effect on weight isn't explained by that mechanism alone. [2, 4]
Tirzepatide acts on two receptors, GIP and GLP-1. This dual activity influences glycemic control and food intake, and it can produce significant reductions in body weight. Having two targets doesn't mean its effect is "double," nor that it's the best choice for everyone: response and tolerance vary. [3]
In practice, feeling less hungry can make it easier to stick to an eating plan. This helps explain why some people manage to sustain changes that used to be very hard for them. The medication modifies part of the biological response that comes with the process; it's still necessary to build a diet that is adequate and compatible with everyday life.
How they relate to Ozempic and Mounjaro
Ozempic contains semaglutide and Mounjaro contains tirzepatide. However, the name of the active ingredient and the brand name are not the same as a universal indication for weight loss.
In the United States, Ozempic and Mounjaro have indications related to type 2 diabetes; Wegovy and Zepbound are brands of semaglutide and tirzepatide, respectively, with indications for weight management. Approvals, dosage forms, and available doses depend on the country. In Argentina, ANMAT announced the registration of Wegovy for weight management in certain people with obesity or overweight and associated conditions. [2–5, 13]
That's why saying a study showed weight loss with semaglutide doesn't mean that result applies to any use of Ozempic. Nor should you swap products or carry their doses over on your own. The choice must follow the local prescribing information and the doctor's evaluation.
What the studies show about weight loss
Clinical trials make it possible to gauge the benefits more precisely than social media testimonials. Three studies help convey the size of the results and their limits.
In STEP 1, adults without diabetes who had obesity, or overweight plus an associated condition, received injectable semaglutide 2.4 mg weekly or placebo, along with a lifestyle intervention. At 68 weeks, mean weight loss was 14.9% of initial weight with semaglutide and 2.4% with placebo. [6]
In SURMOUNT-1, also in adults without diabetes, tirzepatide produced mean weight losses of 15.0%, 19.5%, and 20.9% at 72 weeks, across the 5, 10, and 15 mg dose groups studied. The placebo group lost 3.1%. Participants received guidance on nutrition and physical activity. [7]
The head-to-head comparison came with SURMOUNT-5, published in 2025. In adults with obesity without type 2 diabetes, the mean reduction at 72 weeks was 20.2% with tirzepatide and 13.7% with semaglutide. The trial compared the maximum tolerated doses it had planned for: 10 or 15 mg of tirzepatide versus 1.7 or 2.4 mg of semaglutide, given as weekly injections. [8]
These percentages are group averages, not individual predictions. Nor do they represent every available formulation or dose. The outcome depends, among other factors, on the person's characteristics, continuity of treatment, and tolerance. The doses are mentioned to help interpret the studies, not as instructions for use.
Benefits that go beyond the scale
The clinical interest in these treatments also lies in their effects on associated health problems. In people with type 2 diabetes, semaglutide and tirzepatide can improve glucose control. Evaluating a treatment includes that metabolic response, in addition to the change in weight. [2, 3]
Semaglutide has shown a cardiovascular benefit in a specific population. SELECT studied adults aged 45 or older with established cardiovascular disease, overweight or obesity, and no diabetes. Over a mean follow-up of about 40 months, the combined outcome of cardiovascular death, nonfatal heart attack, or nonfatal stroke occurred in 6.5% of the semaglutide group and 8.0% of the placebo group. The relative risk reduction was 20%, with an absolute difference of 1.5 percentage points. [9]
This distinction matters: the result doesn't mean that everyone who uses semaglutide will have a 20% lower cardiovascular risk. It describes what was observed in a specific population under specific conditions.
With tirzepatide, the SURMOUNT-OSA trials found improvements in the severity of obstructive sleep apnea in adults with obesity and moderate or severe apnea. They evaluated both people who used positive airway pressure and people who didn't. These findings expand the treatment options, but they don't justify abandoning a device or a medical instruction without a reassessment. [10]
The clinical goal thus becomes broader: assessing what health improvements a person can achieve and how to sustain them, instead of judging the whole process by a single number.
Muscle deserves attention during weight loss
Significant weight loss can include both fat and lean mass. Lean mass includes muscle and other tissues; that's why a measurement of lean mass isn't exactly the same as a measurement of muscle lost.
During these treatments, a reduced appetite can make it hard to eat enough. A joint recommendation from nutrition and obesity societies stresses the importance of high-quality nutrition, protein intake tailored to each person, and strength training to help preserve muscle function. Eating less and less should not become the goal. [11]
The activity plan should be adjusted to the person's physical capacity, history, and recovery. It's worth paying attention to strength, performance, and exercise tolerance, in addition to weight. The healthcare team can assess whether persistent fatigue or a marked drop in performance calls for changes. [11]
From my place as a trainer, I consider it essential to support this process with goals the person can sustain. The plan should help them gain confidence in their abilities and recognize progress that also shows in how they move and train.
Why maintenance is part of the treatment
Reaching a certain weight doesn't automatically resolve the tendency to regain it. In the STEP 1 extension, during the year after semaglutide and the structured lifestyle intervention were withdrawn, participants regained, on average, about two-thirds of the weight they had lost. Several cardiometabolic improvements also faded. [12]
This doesn't mean everyone will regain the same amount or that stopping is impossible. It shows why maintenance should be discussed from the start, and why these treatments shouldn't be presented as a fix that lasts a few weeks. Follow-up makes it possible to review the response, side effects, and options when circumstances change.
Decisions about continuing, modifying, or stopping treatment belong to the medical team. Weight regain warrants a reassessment of the plan, without being interpreted as a moral failing or a personal failure.
What responsible use requires
The most common side effects are digestive, such as nausea, vomiting, diarrhea, constipation, and abdominal discomfort. They may appear especially while the treatment is being adjusted. There are also risks that require medical evaluation, including pancreatitis, gallbladder disease, and dehydration with kidney impairment. The risk of hypoglycemia increases when they are combined with certain diabetes treatments. [4]
The US labels contraindicate these medications in people with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2. The warning about thyroid tumors comes from rodent studies; it doesn't show that they cause this cancer in humans. Severe gastroparesis requires special consideration, and these drugs are not used for weight loss during pregnancy. [3, 13]
Before starting, it's necessary to review prior illnesses, other medications, and pregnancy plans. The anesthesia team should also be informed before surgery or any procedure involving sedation. Severe, persistent abdominal pain or vomiting that keeps you from staying hydrated requires medical attention. Combining semaglutide and tirzepatide with each other is not recommended. [4, 13]
Where the medication comes from matters. In Argentina, ANMAT has warned about tirzepatide products without health registration and has reminded the public that registered medications of this type require a prescription and must be purchased at licensed pharmacies. An offer on social media doesn't guarantee quality, authenticity, or proper storage. [14]
A conversation about weight with more evidence and respect
These advances make it possible to talk about obesity with better tools. For a person who meets the clinical criteria, receiving drug treatment can be a legitimate decision within their care. They deserve understandable information and support, without having to justify to others how they are managing their health.
At the same time, a responsible conversation recognizes the differences between people. The best plan should consider the expected benefits, preferences, tolerance, and the ability to keep up with follow-up. A brand's popularity doesn't replace that evaluation.
As a trainer, my contribution is helping build an exercise practice that makes sense for the person and can be maintained; that's why having the right trainer matters. Prescribing and monitoring these medications is the doctor's job, and the nutrition strategy requires support from the appropriate professional. Working in a coordinated way gives each part of the process the attention it needs.
Semaglutide and tirzepatide have opened up important possibilities. Making good use of them means keeping a broad view of health and measuring progress by criteria that go beyond appearance. Everyone deserves to go through this process with information and respect for their own body.
General educational content. It does not replace an individual medical evaluation or constitute a treatment recommendation. Information reviewed on October 3, 2026.
Sources and further reading
[1] World Health Organization. Guideline on GLP-1 therapies for the treatment of obesity, 2025. View source
[2] Ozempic. US prescribing information. View source
[3] Mounjaro. US prescribing information. View source
[4] Wegovy. US prescribing information. View source
[5] ANMAT. Semaglutide and the indications in Wegovy's registration, 2023. View source
[6] Wilding et al. STEP 1. New England Journal of Medicine, 2021. View source
[7] Jastreboff et al. SURMOUNT-1. New England Journal of Medicine, 2022. View source
[8] Aronne et al. SURMOUNT-5. New England Journal of Medicine, 2025. View source
[9] Lincoff et al. SELECT. New England Journal of Medicine, 2023. View source
[10] Malhotra et al. SURMOUNT-OSA. New England Journal of Medicine, 2024. View source
[11] Mozaffarian et al. Joint advisory on nutritional priorities during GLP-1 therapies, 2025. View source
[12] Wilding et al. STEP 1 extension. Diabetes, Obesity and Metabolism, 2022. View source
[13] Zepbound. US prescribing information. View source
[14] ANMAT. Warning about unregistered tirzepatide and sales through pharmacies, 2026. View source
