Someone taking a weight-loss drug might leave half their dinner because they feel comfortably full. They might also stop because they feel nauseous. Measuring the leftovers would reveal the same result, but tell researchers little about why the person stopped eating.
Authors
- Beverley O'Hara
Lecturer in Public Health Nutrition, Leeds Beckett University
- Clarissa Dakin
Post-Doctoral Research Fellow in Appetite Control and Energy Balance, University of Leeds
- Jordan Beaumont
Senior Lecturer in Food and Nutrition, Sheffield Hallam University
That distinction is important when studying how GLP-1 -based medications, including semaglutide and tirzepatide, affect appetite. To understand changes in eating, researchers need to record nausea alongside hunger and fullness, including when it occurs and how severe it is.
Our new review found that studies rarely examined that relationship directly. This leaves uncertainty about how much nausea influenced particular measurements of appetite and food intake.
It does not mean these drugs work mainly by making people feel sick. Separate analyses of semaglutide and tirzepatide trials suggest gastrointestinal side effects, such as nausea and vomiting, explain only a small proportion of weight loss. But understanding people's experience of eating during treatment requires more detailed measurements than many studies currently provide.
Why nausea needs closer attention
GLP-1 is a hormone released by the gut after eating. Medications that mimic its activity help regulate blood sugar and act on systems involved in appetite. They can also slow the movement of food out of the stomach. Tirzepatide , sold as Mounjaro, additionally mimics the activity of another hormone, GIP.
These medications can cause nausea, which may reduce someone's desire to eat. Simply recording that a participant experienced nausea at some point during a trial cannot show whether it affected their eating when researchers measured it.
For that, researchers need to know when nausea occurred and how severe it was. Recording this alongside appetite and food intake could help distinguish feeling satisfied with less food from struggling to eat because of sickness.
Nausea could also lead participants to guess they are receiving the active drug rather than a placebo, a dummy treatment. That awareness might influence their answers to questions about appetite.
However, the limited evidence that directly examined nausea did not consistently suggest it explained changes in eating. One study found similar conclusions after excluding participants who experienced nausea or vomiting. Another found no association between nausea and reduced food intake.
The gap is therefore in understanding nausea's contribution to particular eating measurements, rather than establishing it as the main explanation for weight loss.
What the studies measured
Our review brought together 25 articles involving 4,060 participants, identified through searches conducted in November 2025. It focused on adults who were overweight or obese but did not have diabetes or other major health conditions. So its findings cannot automatically be extended to everyone taking these drugs.
We also conducted meta-analyses, which statistically combine results from comparable studies.
The clearest finding was that people taking GLP-1-based medications consumed fewer calories on average than those in comparison groups, although the size of the difference varied considerably.
Much of this evidence came from laboratory studies. Researchers provided meals and allowed participants to eat as much as they wished, then measured their intake.
These studies offer a controlled way to assess eating, but a laboratory meal cannot capture someone's usual diet over weeks or months. Only two studies in the food-intake analysis used dietary recall, which asks people to remember what they ate. Those studies did not show a clear reduction relative to comparison groups.
That does not establish that the drugs fail to reduce everyday intake. Recalling food consumption accurately is difficult, and two studies provide limited evidence. It does mean that the size and persistence of changes outside the laboratory remain harder to establish.
Appetite beyond the lab
The appetite analysis combined ten studies involving 321 participants. It found a small average increase in appetite suppression: around eight points on a 100-point scale.
Crucially, this analysis measured appetite after meals. It did not include fasting appetite or ratings covering a whole day or the previous week.
Participants marked how hungry or full they felt on a line, a measurement known as a visual analogue scale. These ratings are useful, but may miss changes between meals or in response to everyday situations.
The studies differed in their methods, and we rated the certainty of the appetite evidence as low. The findings cannot establish how strongly these drugs affect appetite throughout daily life, or how much this contributes to weight loss.
Several studies reported reduced food cravings or changes in food reward: how pleasurable or appealing someone finds food, and how strongly they want it.
These findings may overlap with reports of reduced "food noise", a term describing persistent thoughts about food and urges to eat. Researchers have proposed a definition , but its measurement is still developing. Our review did not establish an overall effect on food noise.
Changes in food preferences were also inconsistent. Some studies found reduced liking or wanting for high-fat savoury foods and sweets. Others found broader reductions in interest, including in lower-fat or higher-protein options. Eating less does not necessarily mean eating a healthier diet.
A smaller meal can represent a welcome change for someone who previously struggled to feel satisfied. For someone experiencing nausea, it may reflect difficulty eating enough. Those experiences call for different kinds of support, even if both people are losing weight.
Following eating beyond the laboratory, while recording side effects consistently, would help researchers understand those differences. It could clarify how appetite changes over time and identify people who need help managing side effects or meeting their nutritional needs. Weight loss is an important outcome, but understanding how people feel when they eat would make the evidence more useful to those living with treatment.
Jordan Beaumont receives funding from the National Institute for Health and Care Research (NIHR) and Sheffield Children's Hospital Charity Trust. He is affiliated with the Association for the Study of Obesity and the Faculty of Public Health.
Beverley O'Hara and Clarissa Dakin do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.
