Why overeating on Mounjaro still happens — and what to do about it

What SURMOUNT-1 actually showed about eating behaviour

The SURMOUNT-1 trial, published in the New England Journal of Medicine, followed 2,539 adults over 72 weeks. Participants lost an average of roughly 20–21% of body weight at the 15 mg dose. That result depended in part on a meaningful reduction in calorie intake, tirzepatide's dual GIP and GLP-1 receptor activation slows gastric emptying and amplifies fullness signals after eating. In that sense, the drug does a lot of the heavy lifting on appetite.

What the trial also makes clear is that participants were asked to follow a reduced-calorie diet and increase physical activity alongside treatment. Weight loss was not the medicine acting in isolation. People who continued to eat at their previous volume (particularly high-fat or high-sugar foods) saw less benefit, because energy-dense foods can move through the stomach faster even when emptying is slowed, and the brain's reward circuitry responds to flavour and texture in ways GLP-1 signalling does not fully override.

So overeating on Mounjaro is not a sign the medicine has stopped working. It is usually a sign that food environment and eating habits still need attention alongside the pharmacological support the pen provides.

Why certain foods make overeating easier even on Mounjaro

Tirzepatide slows the rate at which food leaves the stomach. That is part of how it creates fullness. The problem is that liquids and foods with a high fat content empty more quickly than solid, protein-rich meals, a pattern that holds regardless of GLP-1 activity. Highly palatable, ultra-processed foods (think crisps, biscuits, fast food) are engineered to be easy to eat quickly in large quantities. They tend to be energy-dense, quickly digested and strongly rewarding to the brain's dopamine system.

The NHS patient information for tirzepatide advises following a reduced-calorie diet as part of treatment, not as an optional extra. The practical implication: even with appetite noticeably reduced, a meal of dense, palatable food eaten at speed can bypass your fullness cues before the medicine has a chance to register it. Slowing down (putting the fork down between bites, eating off a smaller plate, removing distractions) is not folk wisdom here; it is directly relevant to how the pharmacology works.

It is also worth noting that emotional eating and habitual eating (the 3 pm biscuit, the snack in front of the television) are driven partly by routine and partly by mood, neither of which GIP or GLP-1 signalling fully controls. Those patterns can persist into treatment and account for a meaningful chunk of excess intake even when hunger itself is lower. Guidance on what to eat on Mounjaro covers food choices in more detail.

The practical toolkit: protein, routine and knowing when to pause

Protein is the most evidence-consistent lever available alongside GLP-1 treatment. It is the most satiating macronutrient gram for gram, it supports lean muscle mass during weight loss, and it slows glucose absorption. For people on tirzepatide, adequate protein intake is particularly important because calorie restriction alongside significant weight loss risks muscle loss if protein is low. Our protein guide for people on Mounjaro walks through the numbers in detail. A rough starting point used by many dietitians is 1.2–1.6 g of protein per kilogram of body weight per day, but a prescriber or registered dietitian can personalise that.

Fibre plays a supporting role too. Vegetables, legumes and wholegrains slow gastric emptying further, feed gut bacteria involved in appetite regulation and add volume to meals without adding many calories. Practically, building meals around a protein source and a large portion of vegetables before adding carbohydrates changes the architecture of what you eat without requiring rigid calorie counting.

One concrete habit that helps: keeping a note on the fridge door of what you have planned to eat that day. It sounds mundane, but research on food planning consistently shows it reduces impulsive, high-calorie choices, and on Mounjaro, where nausea is more likely after overeating, the incentive to plan is higher than usual. If overeating is frequent and accompanied by distress, it is worth raising with your prescriber; patterns that look like binge eating deserve clinical attention, not just dietary adjustment.

Questions about eating habits during treatment more broadly, or about appetite being too low, are both common and worth discussing openly. The experience of still overeating further into treatment is also addressed separately for people several months in. If you are still finding your starting dose is not managing appetite well, that is a conversation for your prescriber, dose titration, timing and food choices can all be reviewed together. Check your eligibility and start a free consultation with our clinical team if you have not yet begun treatment.