Experts reveal the seven biggest mistakes people make in Mounjaro

With 2026 now in full swing, many are turning their attention to GLP-1 weight loss medications like Mounjaro, either after starting treatment or seriously considering them.

However, a prominent expert in the field has issued a warning, suggesting that those who use these weight loss jabs consistently fall into the same trap.

Alistair Murray, chief operating officer and weight loss specialist at British digital health company Phlo, regularly advises patients starting GLP-1 treatment.

Former chief pharmacists often see misunderstandings and moments of anxiety, and patients often express regret that they were not aware of these issues before starting their weight loss journey.

Mr Murray has identified seven common mistakes, along with practical advice on how to avoid them.

Mistake 1: Eating out of habit, not because of hunger

“One of the most common things I see is patients saying, ‘I usually have breakfast at this time’ and then eating their usual breakfast, even though they’re not hungry anymore; they’re doing it out of habit,” Mr Murray said.

“The reason GLP-1s are prescribed for weight loss is that they reduce your appetite; they can’t magically change an established habit.

“That moment when you realize your hunger has been quiet is a real opportunity. This is the point where you can stop and ask yourself: Am I eating because my body needs it, or because this is what I’ve been doing? For many people, it’s the first time they’ve ever paused that.

“We often encourage patients to really evaluate their meal. If they had a very carb-heavy breakfast before, this can be an inflection point where they realize they are actually satisfied with something smaller and more protein-dense instead.

“The medicine creates space to make different choices, but you have to be aware of that.”

Mistake 2: Rushing the process because of a deadline

“The scenario we see a lot is people signing up three or four weeks before a wedding or big event and expecting dramatic results, which is simply a bad idea,” Mr Murray said.

“Your body needs time to adapt to GLP-1s. People often have digestive problems, which is the last thing you want on your big day, your appetite needs time to change, and you need time to work out food and daily life for you on this drug. It’s a personal process.

“When people feel it’s ‘not working fast’, it’s often because the goals are set too quickly. We often get people talking to our doctors telling stories they’ve seen online, or results they’ve seen on social media, rather than validating what’s best for their body.

“Slow, steady weight loss is a sign that the treatment is working exactly as it should. Rushing the dose or chasing quick results can backfire harshly and can increase the side effects and make people abandon things that would have worked well if they’d been given time.”

Mistake 3: Assuming side effects start to exist for the long term

“I think the biggest misconception we see is how you feel in the first week is how you will feel on your journey with weight loss drugs,” Mr Murray said.

“It’s no secret that some people can experience diarrhea, nausea, vomiting, or even constipation, and it’s undeniable that it’s a difficult obstacle to overcome, but it’s not forever.

“In fact, side effects are usually most noticeable at the very beginning and often settle as the body adjusts to GLP-1. Small changes in diet, hydration, and routine can make a world of difference.

“Going back to the planning element, seeing maintenance as a priority from day one: make your food solid and light, and you’re a winner.

“Although there are several factors that contribute to this, we see a much higher drop-out rate between the first and second treatment compared to subsequent treatments, which shows that many people who drop out early can still be successful if they reach for additional reassurance and professional support in the first few weeks.

Mistake 4: Not prioritizing protein (then feeling weak, hungry, or ‘stuck’)

“One of the biggest missed opportunities I see is that people eat less overall, but don’t change what they eat, and protein is usually the first thing to drop,” says Mr Murray.

“It can make you tired, less satisfied after eating, and it can make it difficult to preserve muscle when you’re losing weight.

“Protein is your friend during weight loss because it helps with fullness and supports lean mass. The simple rule is to make protein the anchor of every meal.

“Then add color, fiber, and healthy fats around it. Even small upgrades like swapping a carb-heavy breakfast for a protein-first option can make the whole day easier.

“Try to include a source of protein in every meal or snack, such as eggs, yoghurt, chicken, fish, tofu or beans.”

Mistake 5: Cutting back on fiber and water (then blaming medication for constipation, bloating, or feeling ‘off’)

“People are often surprised that deliberate appetite suppression can reduce fiber and fluid intake, simply because you eat less and forget to drink,” says Mr Murray.

“But fiber and hydration are two of the biggest levers for feeling good on your weight loss journey, especially if constipation is an issue.

“Fiber needs water to do its job properly. If one of them is too low, digestion can slow down, and people feel uncomfortable, which can make them stop treatment or throw in the towel.

“A few small habits, like having a water bottle nearby and consuming fiber-rich foods every day, can change the experience.

“Try to build fiber gradually, include vegetables, berries, oats, nuts, lentils, whole grains and chia seeds, and pair it with a steady intake of water.

“Upgrading fiber, however, is not for everyone. This guide is for general information only.

“People with IBS, inflammatory bowel disease, or other digestive conditions should seek advice from a GP, dietitian, or specialist before making dietary changes. Some high-fiber or fermented foods can trigger symptoms in sensitive individuals.”

Mistake 6: Skipping lunch, then ‘saving it’ at night

“A pattern we often see is people barely eat all day because they don’t feel hungry, and then find the afternoon is a danger zone where they crave, snack or eat again,” says Murray.

“It’s not a lack of strength; it’s your body trying to catch up.

“Even if your appetite is low, your body still needs regular meals. A small, protein-based meal earlier in the day can prevent rebound late at night.

“Don’t force yourself to eat purely for the sake of it, but aim to keep your routine stable enough so that you don’t swing from ‘nothing’ to ‘everything’.

“This is a key part of forming new behaviors that will last for years. A light but structured approach works: protein and fiber first, so the evening is calmer.”

Mistake 7: Thinking weight loss is the only metric that matters (and ignoring sleep, strength, and other factors)

“Scale can be beneficial, but it can also be a trap,” Mr Murray said.

“If you only measure success by weekly numbers, you may miss what really predicts long-term results: consistent habits, sleep quality, strength training and how you cope day to day.

“Weight loss caused by fatigue, muscle loss, poor sleep or constant restriction is rarely sustainable.

“We encourage people to track things that support maintenance, such as energy, appetite stability, protein intake, hydration, fiber, and strength.

“The best kind of change is the one you can keep going.

“Try to include two to three strength sessions a week if possible, and protect your sleep. Both of these help to preserve muscle and support appetite regulation.”