You may have heard that nausea is the most talked-about side effect of GLP-1 medications — but constipation is not far behind. Many people starting Wegovy, Ozempic or Mounjaro find that their bowel habits change noticeably in the first weeks of treatment. Stools become harder, less frequent, and sometimes difficult to pass. Understanding why this happens — and what you can do about it — can make a real difference to your comfort and confidence in continuing treatment.

How common is constipation with GLP-1 medication?

Constipation is one of the most frequently reported gastrointestinal side effects of GLP-1 receptor agonists. In the landmark STEP 1 trial (semaglutide 2.4 mg, the active ingredient in Wegovy), approximately 24% of participants reported constipation, compared to 11% in the placebo group. The SURMOUNT-1 trial for tirzepatide (Mounjaro) reported constipation rates of around 17–24% at higher maintenance doses.

In practical terms: if you experience constipation on one of these medications, you are far from alone. It is a recognised, expected side effect — not a sign that something has gone seriously wrong.

Why does GLP-1 medication cause constipation?

GLP-1 receptors are found not only in the pancreas and brain, but throughout the gastrointestinal tract. When the medication activates these receptors, several things happen that slow the movement of food and waste through the bowel:

These effects are dose-dependent: constipation is often most noticeable during dose escalations, when you have just stepped up to a higher strength.

When does constipation typically start?

Most people notice changes in bowel habits within the first two to four weeks of starting treatment, or shortly after a dose increase. This is consistent with the body adapting to GLP-1 activity in the gut.

For some, constipation is only a temporary issue that resolves within a few weeks as the body adapts. For others, it can persist at a lower level throughout treatment — particularly if dietary habits and fluid intake do not change to compensate.

What can you do about constipation?

The good news is that constipation caused by GLP-1 medication is almost always manageable with the right approach. Here are the most effective strategies:

1. Drink more water

This is the single most important change you can make. When stool stays in the colon longer, the colon absorbs more water from it — resulting in hard, dry, difficult-to-pass stools. Aim for at least 2–2.5 litres of water per day (more if you exercise or live in a warm climate). Set a reminder if you find yourself forgetting to drink. Herbal teas and diluted fruit juices also count. Limit caffeinated drinks and alcohol, which can dehydrate you further.

2. Eat more fibre

Dietary fibre adds bulk to stool and helps it move through the intestine. Because you are eating less overall on GLP-1 medication, you may unintentionally consume less fibre. Make a conscious effort to prioritise fibre-rich foods:

Increase fibre gradually — a sudden large increase can cause bloating and gas. If you find it hard to get enough fibre through food alone, a psyllium husk supplement (mixed into a glass of water) is a gentle, well-tolerated option.

3. Keep moving

Physical activity stimulates peristalsis — the wave-like contractions of the intestinal wall that move stool forward. Even a 20–30 minute walk each day can make a meaningful difference to bowel regularity. You don't need intensive exercise; gentle movement is enough to get things moving.

4. Consider a gentle laxative if needed

If lifestyle changes alone are not sufficient, over-the-counter laxatives are safe to use alongside GLP-1 medication. The recommended first step is an osmotic laxative such as polyethylene glycol (PEG / Macrogol), which draws water into the bowel to soften stool. This is a very gentle option that is not habit-forming. Stool softeners (such as docusate) are another mild option. Avoid stimulant laxatives (such as bisacodyl or senna) as a first choice — they are stronger and better reserved for cases where milder options have not worked.

Always speak to your doctor or pharmacist before starting any laxative if you are on other medications or have any underlying conditions.

When should you contact your doctor?

Most cases of constipation on GLP-1 medication are mild and manageable at home. However, you should seek medical advice if:

In rare cases, severe constipation can lead to faecal impaction — a blockage that requires medical treatment. This is uncommon, but is the reason not to ignore prolonged, severe constipation.

Can a dose adjustment help?

If constipation is severe or significantly affecting your daily life, it is worth discussing your dose schedule with your doctor. Slowing the pace of dose escalation — or temporarily staying at a lower dose — can give the gut more time to adapt and often reduces the severity of gastrointestinal side effects, including constipation. This is a recognised and accepted strategy in clinical practice.

Never adjust your dose without first consulting your prescribing doctor.

Does constipation eventually go away?

For many people, constipation improves significantly after the first few weeks as the body adapts to the medication. Symptoms are often most pronounced in the early weeks and after each dose increase. Once you reach your maintenance dose and your gut has adjusted, bowel habits often normalise — especially if you maintain good hydration and fibre intake.

A proportion of people do experience persisting mild constipation throughout treatment. With the right dietary habits, this can usually be managed comfortably without significantly impacting wellbeing.

Medical disclaimer

This article is intended for informational purposes only and does not constitute medical advice. Always consult your doctor or a qualified healthcare professional regarding your specific treatment, symptoms, or concerns. Do not adjust your medication without medical guidance.

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