Constipation with Ozempic, Mounjaro or Wegovy: what can help through diet

Why can GLP-1 medicines cause constipation?

GLP-1 medicines slow stomach emptying and intestinal transit, the same mechanism that promotes fullness and explains nausea [1]. When transit slows, stools spend longer in the colon and lose water. This makes them harder and more difficult to pass. The GLP-1 medicines guide explains how each one works.

There is a second factor too. When you eat less, you take in less fibre than before, even if you do not notice. Very fatty or large meals can slow digestion further [1]. The first step is to keep eating; from there, spread the fibre you are able to manage throughout the day.

Is it temporary, or does it last longer than nausea?

It lasts longer. In trials of semaglutide at doses used for obesity, constipation affected 24.2% of people, compared with 11.1% taking placebo [2]. Each episode lasted a median of 47 days, compared with 2–8 days for nausea, vomiting or diarrhoea [2].

Nausea peaks at around week 20 and then eases. Constipation levels off at around week 10 and continues [2]. It is also among the common digestive side effects of tirzepatide [3]. The Ozempic Summary of Product Characteristics, which covers doses used for diabetes, lists it as a common adverse reaction, affecting up to 1 in 10 people [4]. It is useful to know this from the outset, so you do not simply wait for it to go away on its own.

What can help through diet?

Spreading fibre throughout the day, with a little at each meal, is often easier to tolerate than having it all in one large salad. When your appetite is low, small portions of fruit with the skin on, vegetables, pulses and wholegrain cereals may be easier than a large meal.

Some foods have more specific evidence than fibre in general. The British Dietetic Association’s guide to chronic constipation suggests eating two or three kiwis a day for at least four weeks [5]. It also mentions prunes and rye bread [5]. Kiwi has an advantage when you are eating less, as it takes up little room and can be eaten at any time.

Hydration matters more when you are eating less. If you increase fibre without drinking enough, stools may become even harder. Drink with meals and between meals, taking small sips, as you might when you have nausea.

Movement stimulates intestinal transit. A daily walk is enough; you do not need a strenuous routine. If nausea or tiredness is stopping you from moving much, mention it at your treatment review.

Psyllium may help in some cases of constipation [5]. If you are taking a GLP-1 medicine, check with the person managing your treatment before using it; they can advise you on how to introduce it and how much water you need. For constipation unrelated to medication, see the general constipation guide.

I eat very little. How can I get enough fibre?

This is the question we hear most often in appointments. When your appetite is very low, eating more of anything can be difficult. A practical approach is to choose options with more fibre per mouthful from the small amount you are managing to eat.

A low-appetite day might look like this: yoghurt and a kiwi for breakfast; a pear with the skin on mid-morning; lentil soup and a slice of rye bread for lunch; two prunes and a few walnuts for an afternoon snack; and vegetable purée with fish for your evening meal. For a full week, see what to eat with GLP-1 medicines in a weekly meal plan.

If you are unable to manage enough food for several days in a row, that is the underlying issue. It needs addressing before focusing on fibre, and you should tell your doctor.

Should I increase fibre in the same way if I also feel nauseous?

When nausea and constipation occur together, increasing fibre too quickly can make you feel fuller. So first, we aim for you to eat something at each mealtime, in small portions and with soft textures on days when nausea is worse [1]. Then we gradually add fibre to the meals you tolerate best, over several days.

Vegetable soup, a whole ripe pear or puréed pulses can add fibre without requiring a large meal. Keeping it up every day matters more than the amount on any one day. If nausea is what is limiting you most, the guide to nausea with a GLP-1 medicine can help with that.

Does going to the toilet at the same time each day help?

It often helps. Going at a similar time each day, without rushing or straining, can help train your bowel reflex. This reflex is more likely to be triggered after eating, especially after breakfast. It may take a few days to notice a difference, but it does not depend on how much you eat.

If you feel up to it, a short walk after that meal can add to the effect of movement.

What we see in appointments

The most common mistake is to increase fibre significantly from one day to the next in the hope of a quick fix. This often leads to more bloating and the same constipation. Another is to start taking a laxative recommended by someone you trust without a doctor, pharmacist or dietitian-nutritionist advising you to do so. Some laxatives can cause dependence if used for a long time. Not all are suitable in every clinical situation or alongside every medicine.

We also see people waiting for it to go away on its own, as nausea sometimes does. With this symptom, it is helpful to keep up fibre, water and movement throughout treatment. If you still have constipation after taking these steps for several weeks, speak to your doctor, who can assess whether there may be other causes.