Why your weight fluctuates
- Water and glycogen: At the start you lose a lot of water. If you eat more carbohydrates one day, the stores fill up again – water included.
- Salt: A salty meal holds on to water overnight.
- Digestion: GLP-1 medications slow down the gut – whatever is still in there counts too.
- Cycle and menopause: Hormonal fluctuations lead to water retention.
- New strength training: Muscles temporarily store water after exertion.
How to measure sensibly
- Always the same way: in the morning, after using the toilet, before breakfast
- Compare weekly averages instead of single readings
- Also measure your waist – it often shows fat loss earlier than the scale
- Record your values, e.g. in the Tracker
And if it really stalls?
After a few months the curve flattens out for almost everyone – with less weight, the body also uses less energy. In the pivotal trials, most participants reached a plateau after about a year. Then check honestly: are protein and calories still right? Are you moving enough? Are you sleeping enough? And talk to your doctor rather than changing the dose on your own.
When to see a doctor
- Your weight rises noticeably over several weeks for no obvious reason
- Swelling in the legs or ankles, shortness of breath
- You are thinking about changing the dose
In an emergency: call 112.
FAQ
Why am I suddenly gaining weight in week 3 on Mounjaro?
It is usually water, salt or digestion. What counts is the trend over several weeks, not a single day.
How long does a plateau last?
Short-term stalls often last one to three weeks. After a few months the curve flattens out permanently for almost everyone – that is normal.
Should I increase the dose if I hit a plateau?
That is for your doctor to decide. It is often worth looking at protein, calories, exercise and sleep first.
Sources
This article does not replace medical advice. It does not give any dosing recommendations. As of September 2026.