Wegovy® (injection) and constipation

Three US pools, plus the EU and Canada

Section 6.1 of the US label reports constipation in all three injection safety tables: adults on 2.4 mg for up to 68 weeks, adults randomised to 7.2 mg, 2.4 mg or placebo for 72 weeks, and young people aged 12 and older on 2.4 mg for 68 weeks. ^[1] The EU product information pools STEP 1–4 and the Canadian monograph pools STEP 1–3; both add how long episodes lasted. ^[2][3]

Longer-lasting, and flat across doses

The European and Canadian documents both describe constipation as mild to moderate but of longer duration than the other digestive events. In people treated with semaglutide, the median episode lasted 47 days, compared with 8 days for nausea, 3 for diarrhoea and 2 for vomiting. ^[2][3] That is a median, so half of episodes were shorter, and it says nothing about any one person.

In the 7.2 mg trials, nausea and vomiting rose noticeably from 2.4 mg to 7.2 mg, while constipation barely moved: 19% on 2.4 mg and 20% on 7.2 mg. ^[1] The label reports this without comment. Constipation was still more than twice as common on either strength as on placebo.

One placebo figure stands out: 11% of adults on placebo reported constipation. Section 14.2 explains that everyone in these trials, on medicine or placebo, was asked to follow a reduced-calorie diet and increase activity, and one study began with eight weeks of a low-calorie diet. ^[1] The comparison was between people who all changed how they ate.

Teenagers, and reports after approval

In the adolescent trial, constipation was less common than in adults: 6% on the injection and 2% on placebo. Across that trial, 62% of teenagers on Wegovy® and 42% on placebo reported at least one digestive reaction, and 2.3% versus 1.5% stopped treatment because of one. ^[1]

Section 6.2 lists reactions reported voluntarily once semaglutide was on the market; under digestive disorders it names ileus, intestinal obstruction and severe constipation including faecal impaction. Because these reports come from a population of unknown size, the label says a frequency cannot be estimated reliably and a causal link cannot always be shown. ^[1] The EU table places intestinal obstruction in its “not known” column, and the Canadian monograph lists it among post-market reactions. ^[2][3] Section 5.6 adds that Wegovy® is not recommended in severe gastroparesis. ^[1]

What studies say about blockages

Two kinds of evidence point in slightly different directions, and both are worth seeing. A 2025 meta-analysis of 55 placebo-controlled randomised trials with more than 106,000 participants found that GLP-1 medicines raised the risk of gallstones and probably reflux disease, but probably had little or no effect on intestinal obstruction and most other serious digestive events. ^[5] Trials, however, may be too short or too selective to catch rare events.

A 2023 US health-claims study compared people without diabetes who started semaglutide or liraglutide for weight loss with people on bupropion-naltrexone. The combined GLP-1 group had a higher adjusted risk of bowel obstruction (hazard ratio 4.22), but the confidence interval was wide, and among the 613 semaglutide users in that study no bowel obstruction was recorded; the cases came from the liraglutide group. ^[6] An observational study like this cannot prove cause.

On the more everyday question, a pooled analysis of STEP 1–3 found almost all digestive side effects of semaglutide 2.4 mg, constipation included, were mild to moderate (98.1%), and only 4.3% of people stopped treatment because of them. ^[4]

Possible reasons, from best supported to least

• Label-supported: semaglutide slows stomach emptying and decreases calorie intake (US section 12.2). ^[1] The label does not say which of these, if either, explains constipation.
• Shown in the data but unexplained: constipation was longer lasting than other digestive effects and did not rise with the higher dose. ^[1][2]
• General causes that may overlap: NIH lists eating less fibre, not drinking enough liquids, less physical activity and changes in how much and what you eat among causes of constipation. ^[7] These are general findings, not measurements in Wegovy® users.

Other things that cause constipation

Constipation often has more than one cause. NIH names several medicines and supplements that can make it worse, including aluminium- or calcium-containing antacids, iron supplements, narcotic pain medicines, some antidepressants, calcium channel blockers and diuretics. It also lists pregnancy, travel, ageing, ignoring the urge to go, an underactive thyroid, diabetes, irritable bowel syndrome and blockages of the bowel. ^[7] If constipation started at the same time as another new medicine, both are worth mentioning to your prescriber.

Self-care that general guidance describes

NIH says most constipation can be treated at home by eating more high-fibre foods, drinking plenty of water and other liquids (especially when adding fibre), getting regular physical activity and trying to open the bowels at the same time each day. ^[8] It notes that a health professional may suggest a laxative for a short time and choose the type, and that you should not stop or change a medicine without talking to them first. ^[8]

The Wegovy® label itself says nothing about fibre or laxatives. What it does say is that you should tell your provider about every prescription and over-the-counter medicine, vitamin and herbal supplement, because Wegovy® slows stomach emptying and can affect some medicines. ^[1] Novo Nordisk’s patient page lists constipation among the common side effects to discuss with your healthcare professional. ^[9] So ask your pharmacist or prescriber before starting a laxative or fibre supplement.

Wegovy® is a registered trademark of Novo Nordisk A/S. PepLabo is not affiliated with or endorsed by Novo Nordisk.

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