What Are Obesity and GLP-1 Drugs? — A Letter That Lingers, a Weight That Wants to Return

When Lost Fat Returns

A person who cut back on dinner and increased walking for months to lose weight faces the old number on the scale a year or two later. People around them say it is because they "let go of management," and they easily think so too. Cutting down on meals makes you lose weight in the short term, but diet control alone often does not maintain it for long, and most obese people eventually regain the weight they worked hard to lose (PMID 21677272).

Obesity is a state where fat has excessively accumulated in the body. Regaining weight is often blamed on failing to keep up eating habits and exercise. However, body weight and fat are regulated together by various physiological mechanisms in addition to the food intake and exercise we choose ourselves (PMID 33461826).

These days, the news frequently tells stories of weight dropping significantly through an injection taken once a week. This article follows three things: how obesity is measured, why a body that has lost weight tilts back toward regaining it, and what that injection does and cannot do in the body.

How We Measure Obesity

On your health checkup report, next to your height and weight, there is one more number written. Body mass index is your weight in kilograms divided by the square of your height in meters. If you are 170 cm tall and weigh 87 kg, you get about 30. Because the calculation is easy, it has long been used as the main tool for diagnosing obesity (PMID 42481750, PMID 40831297).

The drug trials we will cover in this article generally recruited adults with a body mass index of 30 or higher, or 27 or higher with at least one weight-related disease (PMID 33567185, PMID 35658024). For Asian populations, a lower cutoff of 25 is sometimes used, and a study analyzing resident cohorts from two regions in China also used this Asian threshold (PMID 41662368).

However, this value only looks at height and weight. It does not fully capture how much fat is present, where it is stored, or whether organs are functioning properly as a result (PMID 42481750). Because it cannot see body composition and fat distribution (PMID 40831297), a person with a lot of muscle and a person with a lot of fat can receive the same number. The same value can overestimate or underestimate actual fat, and the information is insufficient to tell the story of an individual's health (PMID 39824205).

There are proposals to overcome this limitation. A commission formed by the medical journal The Lancet proposed that experts from multiple countries and specialties should go through a consensus process to redefine obesity, and those commissioners included people who have lived with obesity themselves (PMID 39824205). The commission recommended using body mass index only to gauge population risk or for screening, and checking whether fat has accumulated excessively by directly measuring body fat or at least taking an additional body measurement such as waist circumference (PMID 39824205).

This proposal splits obesity into two. Clinical obesity is a state where organs or tissues cannot function properly due to excessively accumulated fat, or where daily activities are significantly limited. The commission views this as a long-lasting chronic disease, much like conditions in other medical specialties (PMID 39824205). Preclinical obesity is a state where fat has accumulated excessively, but the functions of other organs are still preserved. This state generally carries a high risk of progressing to clinical obesity and various diseases (PMID 39824205). In large-scale British population data, people who met the criteria for clinical obesity had a higher risk of cardiovascular disease than people without obesity, and preclinical obesity also showed a slightly higher risk (PMID 42207987).

This definition is still under debate. Although several academic societies have released new diagnostic frameworks beyond body mass index, how to integrate them into clinical practice remains unclear (PMID 42481750). A study that applied this criterion to participants in an obesity drug trial noted that the application was complex even in resource-rich trial settings (PMID 41145317). There are criticisms in the opposite direction as well. The arguments are that broadening the definition of obesity could increase stigma, and that not everyone with a large body size is unhealthy or in need of management (PMID 41277408).

Body mass index is a quick and useful initial yardstick, but it cannot tell the whole story of a person's body, and new definitions beyond it are still in the proposal stage.

Body Weight Is a Value the Brain Defends

If you skip lunch, you start feeling hungry around three or four in the afternoon, and if you eat a hearty dinner, you do not think about food for a while. Hunger and fullness are created by signals traveling from various parts of the body to the brain.

A hormone is a substance made in one part of the body that travels through the blood to a distant site, changing what the cells there do. This series has compared hormones to letters carried by the blood. The letters dealing with appetite come from places all over the body, such as the gut and fat tissue, and go to the brain, which weaves those letters together with neural circuits to regulate how much you eat (PMID 42515672).

The place where the letters gather is deep inside the brain. The hypothalamus is a small area deep in the lower part of the brain that receives nerve signals and sends out hormones. The hypothalamus plays a central role in bringing together signals about the amount eaten, energy coming in and going out, and body weight (PMID 25896063).

Among those letters, we will call out the names of two. Ghrelin is a hormone that comes from the stomach and makes you want to eat. The concentration of ghrelin in the blood drops after a meal, and it strongly increases the amount you eat. Among appetite-related letters, ghrelin is the only one known for making you want to eat, while most of the others are letters that suppress appetite (PMID 24795698).

Leptin is a hormone circulating in the blood in proportion to the amount of fat stored in the body, signaling how much energy is stored in the brain. Leptin enters the brain in proportion to its concentration in the blood and reduces the amount eaten (PMID 24795698). Fullness signals coming from the gut and leptin, which signals the amount of fat, are woven together at the same site in the brain (PMID 18061414). Becoming less responsive to hormones or having weakened fullness signals are cited as factors contributing to obesity (PMID 42515672).

These letters change after you lose weight. In a body that has lost weight, hunger increases and fullness is felt less (PMID 21496461). Although there are differences among individuals, a compensatory shift where hormones that reduce appetite decrease and those that stimulate it increase is a common pattern (PMID 33461826).

If we isolate ghrelin alone, the picture is not simple. In an analysis that gathered fasting blood from people who lost weight by cutting down on meals or increasing exercise, the total amount of ghrelin was increased, and the more weight they lost, the more it increased. However, active ghrelin actually decreased in randomized trials, so the direction conflicted depending on the study design. Changes in other appetite hormones also conflicted (PMID 39929932).

Changes are also reported on the energy expenditure side. Metabolic adaptation is a phenomenon where the energy expended during rest after losing weight becomes lower than expected for the changed body composition. There is a view that this phenomenon explains part of the reason why body weight is regained (PMID 33461826).

The magnitude of that portion lower than expected is under debate. In an analysis re-examining 33 studies, 27 observed this phenomenon, but better-designed studies tended to have smaller values or values that were not statistically distinct, and it seemed to weaken or disappear after body weight stabilized for a while. The authors concluded that higher-quality studies are needed (PMID 33762040).

One review summarized that these changes in a body that has lost weight tilt toward regaining weight, and noted that it is difficult to overcome physiology through behavior alone (PMID 25896063). In a body that has lost weight, hunger increases and fullness is felt less, and these changes tilt toward regaining weight. The extent to which energy is expended even less than expected for the reduced body size is still under debate.

A Advance Letter from the Gut

When breakfast reaches the gut, the gut sends a letter right away. It is the letter that the previous article "How Blood Sugar Stays Steady — A Letter to Store, a Letter to Release" followed.

Blood sugar is the amount of sugar dissolved in the blood. Most of that sugar is glucose, and glucose is sugar produced as carbohydrates in rice, bread, and fruit are digested, in a form that cells can burn for fuel right away. Diabetes is a disease in which the state of blood sugar being higher than the normal range continues for a long time.

The letters dealing with blood sugar mostly go out from one organ. The pancreas is an organ lying horizontally behind the stomach, which concurrently performs the task of making digestive juices and sending them to the gut, and the task of releasing hormones that handle blood sugar into the blood. Insulin is a hormone that comes out of the pancreas when blood sugar rises, and tells the liver, muscles, and fat to "collect and store the glucose in the blood."

There is also a letter in the opposite direction. Glucagon is a hormone that comes out of the pancreas and tells the liver to "take out stored glucose and release it into the blood." And there is a letter that the gut sends to the pancreas. Incretin is a hormone that gut cells release when food touches the gut, giving advance notice to the pancreas that something eaten is coming in. The previous article called incretin an advance letter that calls for more insulin only when blood sugar rises.

GLP-1 is one of the incretins coming from the gut. GIP is another incretin coming from the gut.

GLP-1 has matters outside of blood sugar as well. The action of GLP-1 in reducing the amount eaten and body weight is well preserved in obese animals and humans, in both adolescents and adults (PMID 34626851). Receptors for GLP-1 are widely distributed across the brain and autonomic nervous system outside the pancreas as well (PMID 34626851). GLP-1 is a letter that handles blood sugar, and at the same time, a letter that reaches the amount eaten and body weight.

Drugs Mimicking Letters

Even if the same letter circulates throughout the body, only the cells that recognize the letter read its contents. Receptors are proteins located on cells that recognize and catch only specific hormones. Drug developers used this point.

GLP-1 receptor agonists are drugs made to attach to GLP-1 receptors and produce the same signals as GLP-1. Created by mimicking incretin, they were first used as diabetes treatments and are now also used for obesity treatment (PMID 41931049). After GLP-1 was discovered, efforts continued to extend its lifespan so it could be used for treatment, leading to long-acting drugs following short-acting ones (PMID 31031702). Semaglutide is a GLP-1 analogue designed to stay in the body for a long time by repeatedly binding to and detaching from albumin, a protein in the blood (PMID 31031702), and in trials, it was injected under the skin once a week (PMID 33567185). It is a drug that turned the advance-notice letter the body used to send at meals into a long-lasting letter.

This drug works in various places in the body. Gastric emptying is the process by which the stomach sends food down into the intestines. This drug boosts insulin secretion depending on blood sugar, reduces glucagon secretion, and slows gastric emptying (PMID 34626851). It can also increase fullness by acting directly on nerve clusters in the hypothalamus (PMID 41931049).

The path by which weight decreases is primarily appetite. It is summarized that the effect of reducing weight is handled by GLP-1 receptors in the brain, while the effect of improving blood sugar is handled by receptors in the pancreas (PMID 31031702). In animal experiments, pathways that make the body expend more energy are also treated as important, but what stands out in both animals and humans is the decrease in the amount eaten (PMID 34626851). It is summarized that GLP-1 receptor agonists reduce weight primarily through appetite-suppressing actions and metabolic regulation (PMID 39892489). In several trials, semaglutide reduced hunger and increased fullness, and reduced the amount of energy eaten when people were allowed to eat as much as they wanted (PMID 40107359).

There are also drugs that mimic both letters together. Dual agonists are drugs made to attach simultaneously to the receptors of the two incretins, GIP and GLP-1. Tirzepatide is an example, and both receptors are also located in areas of the brain that regulate the amount eaten (PMID 36050763). However, it is not yet known how much of a role the GIP-side signal plays in humans. GIP reducing the amount eaten and body weight was seen in mice but has not been confirmed in humans, and the authors wrote that important questions regarding the mechanism of action remain (PMID 36050763).

The effects of a drug are measured through comparison. A placebo is a fake drug that looks and is used the same as a real drug but has no medicinal active ingredients. Participants are randomly divided into two groups, one group is given the drug and the other is given a placebo, and the difference between the two is observed.

In a manufacturer-funded trial, when adults with obesity or overweight without diabetes received weekly injections of semaglutide or a placebo along with lifestyle interventions for 68 weeks, body weight decreased by an average of 14.9% and 2.4%, respectively (PMID 33567185). Also in a manufacturer-funded trial, when adults with obesity or overweight without diabetes received tirzepatide or a placebo for 72 weeks, weight decreased by an average of 15.0 to 20.9% depending on the dose in the drug-injected group, and by 3.1% in the placebo group (PMID 35658024).

These values are averages, and the magnitude of decrease varied from person to person (PMID 33567185). In people with diabetes, the extent of weight loss with these classes of drugs was smaller (PMID 39305981). The primary pathway by which these drugs reduce weight is by lowering appetite to reduce the amount eaten, and the difference compared to placebo was measured in trials lasting a little over a year in adults with obesity and overweight without diabetes.

Beyond the Scale on the Scale

A composite of cardiovascular death, non-fatal myocardial infarction, and non-fatal stroke occurred in 6.5% of the semaglutide group and 8.0% of the placebo group (PMID 37952131). The participants were adults aged 45 or older who already had cardiovascular disease such as heart disease or stroke, had a body mass index of 27 or higher, but did not have diabetes. They received semaglutide or a placebo once a week and were followed for an average of over 3 years, and this trial was also funded by the manufacturer (PMID 37952131).

In the same trial, the proportion of people who permanently discontinued the drug due to adverse events was 16.6% in the semaglutide group and 8.2% in the placebo group (PMID 37952131). These results come from people who already have cardiovascular disease, and this trial does not answer whether the same benefits exist for people without such disease. The evidence that semaglutide reduces cardiovascular events had first emerged in people with diabetes, and this trial asked about cases without diabetes (PMID 37952131).

There is also a counterpoint. This is the criticism that most obesity drugs have been approved based on their weight-loss efficacy rather than having their health benefits proven (PMID 41277408). The evidence that cardiovascular events decreased in adults with obesity or overweight without diabetes came from a single trial that followed people with pre-existing cardiovascular disease for over 3 years.

The Toll

The most common side effects are nausea and diarrhea. They are usually temporary, mild to moderate, and subside over time (PMID 33567185). Gastrointestinal side effects were concentrated mainly during the first 20 weeks of increasing the dose (PMID 35658024).

In an analysis pooling 26 randomized trials of overweight and obese adults without diabetes, side effects were common in the drug group but also common in the placebo group. Side effects in the drug group were mostly gastrointestinal symptoms such as nausea, vomiting, diarrhea, and constipation. The authors summarized that discontinuing the drug due to side effects or experiencing serious side effects was rare (PMID 39761578). However, another analysis pooling four semaglutide trials found that discontinuing the drug due to side effects and experiencing serious side effects were greater than with placebo, with serious events primarily involving the digestive, liver, and biliary systems, such as acute pancreatitis and gallstones (PMID 36578889).

Pooling more trials changes the picture slightly. In an analysis pooling placebo-controlled trials across various patient groups including diabetes and obesity (with over 100,000 participants), the risk of gallstones increased by 2 per 1,000 people compared to placebo, and the risk of gastroesophageal reflux disease also likely increased. There appeared to be little to no effect on the risk of other digestive and biliary events (PMID 40499738).

There are also analyses looking at mortality. In another analysis pooling trials of various patient groups at high cardiovascular risk, including people with diabetes, deaths and major cardiovascular events were reduced compared to the control group, at the cost of increased gastrointestinal and gallbladder diseases, with no difference in pancreatitis (PMID 40892610). The cardiovascular benefits of this class of drugs have been reported particularly in people with diabetes, and because this analysis also mixed various patient groups, the results are not exclusively for obese adults without diabetes (PMID 40892610).

Not all of the lost weight is fat. Lean body mass is the weight that remains when fat is subtracted from total body weight, which includes muscle and bone. The fact that muscle and bone may also decrease together is cited as a side effect of these drugs, and what that loss means for bodily function remains an open question (PMID 41931049). Some studies have reported that lean body mass decreases significantly and is associated with a pathological loss of muscle. Conversely, animal experiments and limited clinical data have results pointing toward muscle preservation. A brief narrative review summarizing these data concluded that more research is needed (PMID 41022269).

The most common toll is gastrointestinal symptoms, there are rarely increased risks such as gallstones, and what the potential muscle loss means does not yet have an answer.

When You Stop

People who had lost a large amount of weight over 68 weeks through semaglutide and lifestyle intervention stopped both. One year later, they regained two-thirds of the weight they had lost, and most of the heart and metabolic markers that had improved returned toward their starting states (PMID 35441470). Still, they remained an average of 5.6% lighter than at the beginning (PMID 35441470). This observation followed a portion of the original trial participants, and the analyses were all exploratory. The authors concluded that these results confirm obesity is chronic, and suggest that treatment must be continued to maintain improvements in weight and health (PMID 35441470).

There are also trials where participants were made to stop at random. Adults with obesity or overweight without diabetes took tirzepatide for a little over eight months to lose an average of 20.9%, after which those who finished this period were randomly divided into two: one side kept taking it and the other side was switched to a placebo, and they were followed for another year. Both groups received diet and physical activity management together. The group that kept taking it lost an additional 5.5%, while the group switched to a placebo regained 14.0% (PMID 38078870). Even the placebo group was an average of 9.9% lighter than when they first started (PMID 38078870).

A pooled analysis of weight changes after stopping concluded that meaningful weight regain appeared regardless of drug type, study design, and region, and its magnitude followed the size of the initial effect (PMID 42534203). Most studies included in this analysis looked backward at past records, and the differences between studies were also large (PMID 42534203). The authors interpreted these results as evidence that anti-obesity drugs should also be viewed through a model of long-term use like medicines for other chronic conditions, and noted that future trials should plan follow-up after stopping from the beginning (PMID 42534203). This is not a conclusion that determines who should use them and for how long.

Interpretations vary. One review explained this weight regain as the body's adaptation to weight loss—in other words, the turning back on of appetite-stimulating pathways and an adaptation to use less energy—and noted that there is no yet-proven method of tapering off and stopping the drug (PMID 41889156). An editorial argued that this should be understood as a disease relapse, using it as grounds to view obesity as a long-lasting, recurring disease (PMID 41909366).

When you stop the medication, much of the lost weight returns, but on average you remain lighter than at the start.

The Phrase "You Lack Willpower"

Some people postpone visiting the hospital because of their weight. Stigma in the clinic acts as a barrier that blocks communication with medical staff, reduces the quality of care, and causes patients to avoid hospitals (PMID 37197883). Attitudes that look down on people with obesity also appear among medical staff across various specialties and clinical settings (PMID 37197883).

Weight stigma is the act of overlaying negative judgments and stereotypes onto a person on the grounds of their weight. People with obesity commonly experience discrimination at work, at school, and in hospitals (PMID 32127716). An international consensus statement created by experts from multiple countries reviewed studies showing that weight stigma can harm the body and mind and that individuals experiencing stigma are less likely to receive proper treatment, and concluded that weight stigma harms health, violates human and social rights, and is unacceptable (PMID 32127716).

At the root of this stigma is the idea that obesity is an individual's responsibility. Obesity arises from a complex tangle of genetic and environmental factors, and most of those factors are outside the scope of what a single person can control. Stigma does not prevent obesity either (PMID 36781624). A gap still remains between studies showing that obesity is a chronic disease and society's perception (PMID 39919880).

Even after drugs emerge, this problem remains. When treatment is framed in the language of morality or behavior, it has been pointed out that broadening the definition of obesity could further entrench stigma (PMID 41277408). Behind weight regain lies a biology beyond willpower, and the position of the international consensus statement is that weight stigma is harmful in its own right.

One Breakfast, in a Body Where the Letter Lingers

The previous article followed how a healthy body receives a single breakfast. We follow the same breakfast again, this time in the body of someone who takes a GLP-1 receptor agonist once a week. The injection was given a few days ago, and the drug is designed to stay in the body for a long time (PMID 31031702).

At seven-thirty in the morning, they eat a breakfast of rice and side dishes. The stomach sends food down into the intestine more slowly than usual (PMID 34626851). When digested sugar enters the blood and blood sugar rises, the drug increases insulin secretion and reduces glucagon secretion in response to that blood sugar (PMID 34626851). The condition for the advance letter—calling for more insulin when blood sugar rises—carries over into the drug as well.

At the same time, the drug acts on nerve clusters in the hypothalamus to increase fullness (PMID 41931049). When lunchtime arrives, hunger is milder, and even when allowed to eat freely, the amount eaten decreases (PMID 40107359). The primary way weight is lost in humans is through this reduction in food intake (PMID 34626851, PMID 39892489). As days like this continue for several months, weight decreases.

During the first few months, gastrointestinal symptoms such as nausea or diarrhea may accompany it, and they usually cluster during the period of increasing the dose before subsiding (PMID 33567185, PMID 35658024).

This person continues the injections along with lifestyle interventions for a little over a year, and then stops both together. For people who stopped both the drug and lifestyle interventions after 68 weeks of treatment, a significant portion of the lost weight returned about a year later, and most indicators that had improved reverted toward where they started (PMID 35441470). One review explains the regain after stopping as an adaptation of the body that lost weight—namely, that pathways stimulating appetite turn back on and adaptations to expend less energy occur (PMID 41889156). Still, on average, they remained lighter than at the start (PMID 35441470, PMID 38078870).

Where to Look Next

How to maintain weight lost after stopping, and what potential muscle and bone loss means for bodily function over the long term, are questions that do not yet have answers (PMID 41931049).

The basics of letters and recipients are covered in "How Hormones Work — Letters Only the Addressee Reads, Replies That Say Stop", and the normal operation of how incretins handle blood sugar is covered in "How Blood Sugar Stays Steady — A Letter to Store, a Letter to Release". The relationship between weight and diabetes, and the stigma surrounding diabetes, are taken over by "What Is Diabetes? — The Letter That Never Comes, the Letter That Isn't Read".

Source Papers

• "Biology's response to dieting: the impetus for weight regain." (2011) — PMID 21677272 — Dietary restriction has a low long-term success rate for weight loss, and most people regain the weight; the authors conclude that biological adaptations are comprehensive, sustained, and redundant.
• "Mechanisms of weight regain." (2021) — PMID 33461826 — Weight regain is often blamed on a lack of compliance, but body weight and fat are regulated by physiological mechanisms; appetite-suppressing hormones decrease while appetite-stimulating hormones increase (with individual variation); this defines metabolic adaptation and helps explain some of the phenomenon.
• "Diagnosis, staging and management of obesity: a synthesis of contemporary guidelines." (2026) — PMID 42481750 — BMI has been the primary diagnostic tool, but it fails to reflect fat mass, distribution, or organ function; it remains unclear how a new diagnostic framework will be integrated into clinical practice.
• "Once-Weekly Semaglutide in Adults with Overweight or Obesity." (2021) — PMID 33567185 — In 1,961 adults without diabetes who had a BMI ≥30 (or ≥27 with a comorbidity), combined with lifestyle intervention for 68 weeks, weight change was −14.9% versus −2.4%; nausea and diarrhea were common, temporary, and mild to moderate.
• "The impact of the Lancet Commission definition of obesity on its prevalence ... in East Asians" (2026) — PMID 41662368 — In two Chinese community cohorts using the Asian BMI cutoff of ≥25, applying the new definition leads to some reclassification (observational study, limited to Chinese participants).
• "From Old to New: A Comprehensive Review of Obesity Diagnostic Criteria and Their Implications." (2025) — PMID 40831297 — BMI fails to capture body composition, fat distribution, metabolic health, or functional impairment; the new criteria require further validation.
• "Definition and diagnostic criteria of clinical obesity." (2025) — PMID 39824205 — A committee (consisting of 58 experts and individuals with lived experience) proposes clinical and preclinical definitions of obesity, recommending BMI for populations and screening, alongside additional measurements such as waist circumference.
• "Implications of Lancet framework definition of obesity in relation to cardiovascular diseases." (2026) — PMID 42207987 — In the UK Biobank, the risk of cardiovascular disease is higher under the clinical obesity definition (observational).
• "Application of the Lancet Commission Criteria for the Diagnosis of Obesity to a Clinical Trials Population: The LEAP Trial." (2026) — PMID 41145317 — Applied to 860 trial participants, showing that the criteria are complex to implement even in resource-rich settings.
• "[Expanding definition of obesity risks reinforcing stigma]." (2025) — PMID 41277408 — Expanding the definition risks reinforcing stigma; most obesity medications are approved for their effects on weight rather than health benefits; not all large bodies are unhealthy.
• "Peptide Hormones in Appetite Regulation: A Complex Network." (2026) — PMID 42515672 — Peripheral signals such as ghrelin, GLP-1, PYY, leptin, and insulin are integrated by hypothalamic and brainstem circuits; hormone resistance and impaired satiety signals contribute to obesity.
• "Physiological adaptations to weight loss and factors favouring weight regain." (2015) — PMID 25896063 — The hypothalamus integrates signals for intake, energy balance, and body weight; physiological adaptations after weight loss favor weight regain, leading to the assessment that behavior struggles to overcome physiology.
• "Fasting appetite-related gut hormone responses after weight loss induced by calorie restriction, exercise, or both" (2025) — PMID 39929932 — Total ghrelin increases after weight loss (with greater increases following larger weight loss), while findings for active ghrelin are mixed, decreasing in randomized controlled trials and increasing in non-randomized studies; results for other hormones are similarly mixed.
• "Is your brain to blame for weight regain?" (2011) — PMID 21496461 — In the weight-reduced state, hunger increases and satiety decreases, accompanied by changes in leptin and meal-related gut peptides.
• "Does adaptive thermogenesis occur after weight loss in adults? A systematic review." (2022) — PMID 33762040 — Observed in 27 out of 33 studies, but small or negligible in well-designed studies, and attenuates during weight stabilization; high-quality research is needed.
• "GLP-1 physiology informs the pharmacotherapy of obesity." (2022) — PMID 34626851 — GLP-1 receptor agonists cause glucose-dependent insulin secretion, glucagon reduction, and delayed gastric emptying; their effects on reducing food intake and body weight are preserved in animals and humans; receptors are widely distributed in the central and autonomic nervous systems; reduction in food intake is important in humans.
• "GLP-1 Receptor Agonists." (2026) — PMID 41931049 — Incretin mimetics; induce satiety by reducing gastric emptying, suppressing glucagon, and acting directly on the hypothalamus; side effects are primarily gastrointestinal, with potential muscle and bone loss; the long-term meaning of adherence, weight regain after discontinuation, and musculoskeletal loss remains unresolved.
• "Neuroendocrine control of food intake." (2008) — PMID 18061414 — Gastrointestinal satiety signals (such as GLP-1) are integrated via the vagus nerve and brainstem in the arcuate nucleus alongside fat signals like leptin and insulin.
• "Peptides and food intake." (2014) — PMID 24795698 — Ghrelin is secreted by the stomach, decreases after meals, and is the only known circulating molecule that strongly increases food intake; leptin and insulin circulate in proportion to body fat and enter the brain to reduce food intake.
• "The Discovery and Development of Liraglutide and Semaglutide." (2019) — PMID 31031702 — Efforts to extend the half-life of GLP-1 led to long-acting analogs sustained by reversible albumin binding; weight effects occur via receptors in the brain, while blood glucose effects occur via receptors in the pancreas; weight loss is driven by a reduction in energy intake.
• "Mechanisms of GLP-1 Receptor Agonist-Induced Weight Loss" (2025) — PMID 39892489 — Weight loss is achieved primarily through appetite suppression and metabolic regulation.
• "Exploring beyond numeric weight loss: The metabolic effects of semaglutide." (2025) — PMID 40107359 — Across multiple trials, ad libitum energy intake decreases, hunger decreases, and satiety increases; weight is regained upon discontinuation.
• "Tirzepatide, a dual GIP/GLP-1 receptor co-agonist ..." (2022) — PMID 36050763 — Designed to activate both GIP and GLP-1 receptors, which are also expressed in brain regions that regulate food intake; GIP-induced reductions in food intake and body weight occur only in rodents, leaving important questions about its mechanism of action.
• "Tirzepatide Once Weekly for the Treatment of Obesity." (2022) — PMID 35658024 — In 2,539 adults without diabetes over 72 weeks, weight change by dose was −15.0% to −20.9% versus −3.1%; gastrointestinal side effects were common, primarily during the dose-escalation phase.
• "Seven glucagon-like peptide-1 receptor agonists and polyagonists for weight loss ..." (2024) — PMID 39305981 — Weight loss effects are smaller in patients with type 2 diabetes.
• "Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes." (2023) — PMID 37952131 — In 17,604 adults aged 45 or older with pre-existing cardiovascular disease, a BMI ≥27, and no diabetes, over a mean of 39.8 months, major adverse cardiovascular events were 6.5% versus 8.0%; permanent discontinuation due to adverse events was 16.6% versus 8.2%.
• "Efficacy and Safety of Glucagon-Like Peptide-1 Receptor Agonists for Weight Loss Among Adults Without Diabetes" (2025) — PMID 39761578 — Across 26 randomized controlled trials involving 15,491 individuals, side effects were common and predominantly gastrointestinal, while discontinuation and serious adverse events were rare; the authors conclude that the treatment is effective and safety concerns are mainly gastrointestinal.
• "Efficacy and Safety of Semaglutide for Weight Loss in Obesity Without Diabetes: A Systematic Review and Meta-Analysis." (2022) — PMID 36578889 — Across 4 randomized controlled trials, gastrointestinal side effects, discontinuations, and serious adverse events (such as acute pancreatitis and cholelithiasis) were more frequent with the drug than with placebo.
• "Glucagon-Like Peptide-1 Receptor Agonists and Gastrointestinal Adverse Events" (2025) — PMID 40499738 — Across 55 randomized controlled trials involving 106,395 individuals, gallstones increased by 2 cases per 1,000, and there was a possible increase in gastroesophageal reflux, with little effect on other gastrointestinal or biliary events.
• "Cardiovascular Effects and Tolerability of GLP-1 Receptor Agonists: A Systematic Review and Meta-Analysis of 99,599 Patients." (2025) — PMID 40892610 — Across 21 randomized controlled trials (including various high-risk patient groups such as those with diabetes, with benefits reported especially in diabetes), deaths and major adverse cardiovascular events were reduced, gastrointestinal and gallbladder disorders were increased, and no difference was found in pancreatitis.
• "GLP-1 receptor agonists and sarcopenia: Weight loss at a cost? A brief narrative review." (2025) — PMID 41022269 — Some studies indicate reductions in lean mass and potential links to sarcopenia, whereas preclinical and limited clinical data suggest preservation is possible, requiring further research.
• "Weight regain and cardiometabolic effects after withdrawal of semaglutide: The STEP 1 trial extension." (2022) — PMID 35441470 — In 327 participants (exploratory), two-thirds of the lost weight was regained one year after discontinuation, cardiometabolic risk markers returned toward baseline, and the net weight loss was 5.6%; the authors conclude this confirms the chronicity of the condition and suggests the need for continued treatment.
• "Continued Treatment With Tirzepatide for Maintenance of Weight Reduction ... SURMOUNT-4" (2024) — PMID 38078870 — After a 36-week run-in period resulting in a −20.9% weight change, continuation for 52 weeks yielded a change of −5.5% versus +14.0% for placebo, while the placebo group also showed a change of −9.9% from weeks 0 to 88; diet and physical activity were maintained.
• "Post-cessation Weight Regain After Weight Management Medications: A Systematic Review and Meta-Analysis." (2026) — PMID 42534203 — Across 17 studies (11 retrospective), weight regain occurred regardless of the medication, study design, or region, with the magnitude tracking the initial treatment effect and substantial heterogeneity; the authors interpret this as supporting a long-term pharmacotherapy model akin to chronic disease management, and recommend tracking post-discontinuation follow-up as an essential outcome.
• "Clinical Management of Weight Regain and Cardiometabolic Consequences After Discontinuation of GLP-1 Receptor Agonists." (2026) — PMID 41889156 — A narrative review noting that weight regain reflects biological adaptations such as the reactivation of appetite-stimulating pathways and adaptive thermogenesis, with no validated tapering strategies currently available.
• "Weight Regain After GLP-1-Based Therapy Discontinuation: Failure, Physiology, or Follow-Up Gap." (2026) — PMID 41909366 — An editorial arguing that weight regain following discontinuation should be understood as a disease relapse rather than treatment failure.
• "Weight Stigma and Barriers to Effective Obesity Care." (2023) — PMID 37197883 — Stigmatizing attitudes among healthcare providers create barriers including poor communication, reduced quality of care, and healthcare avoidance.
• "Joint international consensus statement for ending stigma of obesity." (2020) — PMID 32127716 — Highlights discrimination in the workplace, education, and healthcare, resulting in physical and psychological harm and reduced likelihood of receiving appropriate treatment; reaches a consensus that weight stigma is unacceptable.
• "Obesity Stigma: Causes, Consequences, and Potential Solutions." (2023) — PMID 36781624 — Obesity is largely the result of interactions between genetic and environmental factors outside of individual control; personal responsibility framing generates stigma, and stigma does nothing to prevent obesity.
• "Weight Stigma." (2025) — PMID 39919880 — Highlights the disconnect between societal perceptions and research establishing obesity as a chronic medical condition.