Constipation on Ozempic: the fibre and water that help

Constipation is the side effect nobody mentions at the start, and one of the most common a few weeks in. It is not a sign that something has gone wrong. Slowing the gut is part of how these medications work, and a slow gut with less in it is a constipated gut. This page is about what the labels say, what actually helps, and when it stops being a self-help matter.

Why it happens

A GLP-1 medication slows how fast your stomach empties and how quickly food moves along the gut. That is a large part of why you feel full for so long. The same slowing gives the large bowel more time to draw water out of what is passing through it, so what arrives at the end is drier and harder.

Two other things stack on top. You are eating less, so there is less bulk to move, and a bowel with little in it moves slowly. And with the appetite gone, thirst tends to go quiet too, so most people drink less without noticing. Less fibre, less water, a slower gut: that is the whole mechanism, and each part of it can be worked on.

How common it is

Common enough to be in every label.

• In the Wegovy trials in adults with obesity, 24 in 100 people reported constipation, against 11 in 100 on placebo.¹
• On Ozempic for type 2 diabetes, 5 in 100 at 0.5 mg and 3 in 100 at 1 mg, against 1.5 on placebo.²
• On Zepbound for weight, 17 in 100 at 5 mg, 14 at 10 mg and 11 at 15 mg, against 5 on placebo.³
• On Mounjaro for type 2 diabetes, 6 to 7 in 100, against 1 on placebo.⁴

The weight-loss doses run higher than the diabetes doses, and the numbers follow. Like the nausea, it tends to be worst in the first weeks on a new dose and to ease as the gut adjusts, which is worth knowing on a bad week.

Fibre, with a number

The recommended fibre intake for adults is 25 grams a day for women and 38 for men, or 14 grams for every 1,000 calories eaten.⁵ Most people were not getting there before the medication; the average American adult eats about 17 grams.⁵ On a GLP-1 the gap widens, because half the food means half the fibre.

That 14-grams-per-1,000-calories rule is the useful one when you are eating little. If your day is 1,200 calories, the target is about 17 grams, which is reachable. Where it comes from:

• A bowl of oats: about 4 grams. With a tablespoon of chia on top, closer to 8.
• Half a cup of cooked lentils or beans: 6 to 8 grams. Beans in a soup are the easiest fibre on a small appetite.
• An apple or a pear with the skin, or two kiwis: about 4 grams each.
• A cup of berries: about 4 grams; raspberries nearer 8.
• Vegetables at every meal, the tougher the better: broccoli, carrots, cabbage.
• Bread and rice: the whole-grain kind, always, since they are half the fibre or none.

Go up slowly, a few grams a week. A jump from 10 to 30 grams overnight on a slow gut is a bloated, windy week. And every gram of fibre needs water, or it makes things worse rather than better; the gut doctors say the same.⁶

Water, movement, a routine

Water through the day. Thirst is unreliable on these medications, so do not wait for it. A glass on waking, one with each meal, one mid-morning and mid-afternoon, and you are at six or seven before the evening. Sipped, not downed, on the days the stomach is slow. Tea and soup count.

Move. A walk after a meal does more for a slow gut than most people expect. Twenty minutes is enough. The bowel likes movement of the whole body.

Give it a time. The gut works on habit. After breakfast is the strongest natural signal of the day; a few unhurried minutes then, every day, whether or not anything happens, and after a week or two it tends to start happening. Feet up on a small stool helps more than it should.

Do not ignore the urge. On a slow gut the urge comes rarely. When it comes, go.

What the gut doctors say works

The 2023 guideline from the two American gastroenterology societies on chronic constipation is about medicines, but it starts with fibre. It suggests fibre supplementation, and of the supplements it looked at, psyllium is the one with evidence; bran and inulin had very little. It says to drink plenty with it, and that wind is a common price.⁶ The guideline also names over-the-counter options with good evidence, polyethylene glycol most strongly, magnesium oxide and senna with more caution.⁶ Which of those, at what amount and for how long, is a question for your pharmacist or your prescriber. A gut slowed by medication is not an ordinary slow gut, and they will want to know what you are on.

One more thing with real evidence and no pharmacy: kiwifruit. In a 2023 international trial of people with constipation, two green kiwis a day for four weeks increased complete bowel movements and improved abdominal comfort, and it held up against psyllium.⁷ Two kiwis is a small, cold, easy thing to eat on a GLP-1, which is why it is on this page.

When to call your prescriber

Constipation that answers to fibre, water and a walk is a side effect. These are not, and they need a call:

• No bowel movement for several days together with belly pain that is getting worse.
• A hard, swollen belly, being unable to pass wind, or vomiting. The Wegovy label lists intestinal obstruction, ileus and severe constipation with faecal impaction among the reports since it was approved, and those need a doctor the same day.¹
• Blood when you go, or black stools.
• Constipation that started with the medication and has not eased at all after the first month on a dose, despite the above.

Tilly counts fibre and water on Today, next to the protein, and says how much of each is left before the evening. It never tells you what dose to take. It just keeps the boring numbers in front of you, which for this particular problem is most of the cure.