A small number with a large ratio
In Table 1 of the US prescribing information, constipation is the last digestive row: 5% on both doses against 1% on placebo, across five glycemic control trials in adults. [1] The absolute numbers are small, but five times the placebo rate is a clear difference. Unlike nausea or vomiting, the US pool shows no extra step between 1.2 mg and 1.8 mg.
| Group | People in group | Reported constipation |
|---|---|---|
| Placebo | 661 | 1% |
| Liraglutide 1.2 mg | 645 | 5% |
| Liraglutide 1.8 mg | 1,024 | 5% |
What other trials recorded
The Canadian monograph shows constipation trial by trial, counted regardless of what investigators thought caused it. [3] The spread is wide. In LEAD-2 the middle dose had the highest rate, in LEAD-3 the top dose did, and in LEAD-5 nobody on placebo reported it. [3] The European summary places constipation in its common class, between 1 in 100 and 1 in 10 people. [2]
| Trial and background | Victoza® | Comparison |
|---|---|---|
| LEAD-2, 26 weeks, with metformin [3] | 0.6 mg 2.1%; 1.2 mg 4.6%; 1.8 mg 2.5% | Placebo 1.7%; glimepiride 1.7% |
| LEAD-5, 26 weeks, with metformin and glimepiride [3] | 1.8 mg 2.2% | Placebo 0.0%; insulin glargine 0.9% |
| Trial 1860, 26 weeks, with metformin [3] | 1.2 mg 4.5%; 1.8 mg 5.0% | Sitagliptin 2.7% |
| Trial 1842, 52 weeks, 1.8 mg with metformin [3] | 2.5%; 3.1% with insulin detemir added | No placebo arm |
| LEAD-3, 52 weeks, Victoza® alone [3] | 1.2 mg 8.4%; 1.8 mg 11.4% | Glimepiride 4.8% |
| EU frequency class [2] | Common (1 in 100 to 1 in 10) | — |
The rare serious end
Section 6.2 of the US label lists reports received after approval, which cannot give a rate or prove cause: ileus, intestinal obstruction and severe constipation including faecal impaction are among them. [1] Canada says delayed gastric emptying, intestinal obstruction and ileus have been reported in its postmarketing database. [3] The European table rates intestinal obstruction as rare, between 1 in 10,000 and 1 in 1,000 people, and its leaflet describes it as a severe form of constipation with stomach ache, bloating and vomiting. [2]
Research points in two directions. A 2025 systematic review that pooled six studies with over half a million people found no significant overall increase in bowel obstruction or ileus with GLP-1 medicines, with very high variation between studies, but the liraglutide subgroup showed about three times the odds. [4] That analysis mixed trials with cohort and case-control studies, which can show association but not cause. A separate 2025 meta-analysis of 55 placebo-controlled randomised trials found that GLP-1 medicines probably have little or no effect on intestinal obstruction and similar events. [8]
Why it might happen
Label-supported: Victoza® slows stomach emptying as part of its effect on blood sugar after meals. [1] The labels do not describe a separate effect on the large bowel, so this explains slower digestion in general rather than constipation specifically.
Plausible but not measured: decreased appetite affected 10% of people on 1.2 mg and 9% on 1.8 mg in the US pool. [1] NIDDK lists not eating enough fibre and not drinking enough liquids among causes of constipation. [5] Eating and drinking less on Victoza® could therefore contribute, but none of the sources measured that link.
Reported in research: the liraglutide signal for obstruction and ileus comes largely from observational data and has not been confirmed by randomised trials. [4][8]
Other reasons for constipation in diabetes
NIDDK lists a long set of causes, several of them common in people with type 2 diabetes. Conditions that affect metabolism, such as diabetes, and hormone conditions, such as an underactive thyroid, are on it. [5] So are medicines and supplements: calcium channel blockers and diuretics for blood pressure, iron supplements, antacids containing aluminium or calcium, opioid pain medicines and some antidepressants. [5] Changes in routine, travel, ignoring the urge to go, low physical activity and irritable bowel syndrome complete the list. [5]
What the sources describe
- Movement and fluids: MedlinePlus suggests regular exercise and drinking more water. [6] The Victoza® Medication Guide also asks you to drink fluids to lower the risk of dehydration. [1]
- Fibre, slowly: MedlinePlus advises adding fibre-rich foods gradually because more fibre can cause gas and bloating, and drinking plenty of water when you do. [6]
- Routine: going when you feel the urge, trying the same time each day and not skipping meals. [6]
- Laxatives with care: MedlinePlus says not to take a laxative if you have severe stomach pain, nausea or vomiting, and to check with your provider before using one for more than a week; children should not be given laxatives or enemas without asking their provider. [6][7]
- Your medicine list: since many medicines contribute, a pharmacist can check what else you take. [5]
Victoza® is a registered trademark of Novo Nordisk A/S. PepLabo is not affiliated with or endorsed by Novo Nordisk A/S.
When to get help
| Sign | Who to contact | How fast | Source |
|---|---|---|---|
| Constant belly pain with constipation, swelling, vomiting or being unable to pass wind | Urgent medical care | Emergency | NIDDK [5]; EU leaflet [2] |
| Severe stomach pain that does not go away, possibly reaching the back | Stop Victoza® and call your provider straight away | Emergency | Medication Guide [1] |
| Bleeding from the rectum or blood in the stool | See a doctor right away | Today | NIDDK [5] |
| Constipation with fever, lower back pain or weight loss you were not trying for | See a doctor right away | Today | NIDDK [5] |
| No bowel movement for 3 days, or bloating and stomach pain | Contact your provider | Today | MedlinePlus [6] |
| Constipation that keeps coming back on Victoza® despite self-care | Raise it with your prescriber | At your next appointment | Medication Guide [1]; NIDDK [5] |
