Weight loss medications have become an increasingly common part of managing obesity and related health conditions. Drugs such as semaglutide and liraglutide, often prescribed under brand names like Wegovy, have shown impressive results in helping patients lose weight and improve metabolic health. For many, they can be life changing.
However, like any medication, they come with side effects, like digestive issues. Patients may notice changes in bowel habits, discomfort, or other symptoms without immediately linking them to their medication. Understanding how these treatments affect the gut can help patients manage symptoms.
Why weight loss medications affect the gut
Most modern weight loss medications belong to a class known as GLP-1 receptor agonists. These drugs mimic a natural hormone that helps regulate appetite, blood sugar, and digestion. One of their key effects is slowing down how quickly food leaves the stomach, helping people feel fuller for longer.
While this is beneficial for weight loss, it also has a direct impact on bowel function. Slower movement through the digestive tract can lead to constipation, while changes in gut signalling can cause nausea, bloating, or diarrhoea in some people.
A large 2025 systematic review involving more than 33,000 patients confirmed that gastrointestinal symptoms are the most common side effects of these medications. Nausea, vomiting, diarrhoea, and constipation were frequently reported.
Constipation and its knock-on effects
Constipation is one of the more overlooked side effects, but it can have a significant impact on comfort and quality of life. Studies suggest that around 24% of people taking semaglutide (Wegovy) experience constipation. For some, this may be mild and temporary. For others, it can become persistent and uncomfortable.
When bowel movements become less frequent or more difficult, patients may find themselves straining. Over time, this can lead to additional problems such as haemorrhoids, anal discomfort, or even small tears in the lining of the anus.
Weight loss medications and the gut microbiome
Another area of growing interest is how these medications interact with the gut microbiome. A 2025 systematic review explored this relationship and found that GLP-1 medications may influence the composition of gut bacteria, although results varied depending on the population studied and how long the medication was used.
Some changes in the microbiome may support weight loss and metabolic improvements. However, shifts in bacterial balance can also contribute to digestive symptoms such as bloating or altered bowel habits. This is an evolving area of research, but it reinforces the idea that these medications influence the entire digestive environment, not just the appetite.
Expert advice for bowel symptoms
If you’re taking weight loss medication and notice changes in your bowel habits, simple measures can often help. Staying well hydrated, gradually increasing fibre intake, and maintaining regular physical activity can support bowel function. If constipation becomes persistent or leads to pain, bleeding, or significant discomfort, it’s important to seek medical advice. There may be additional treatments or strategies that can ease symptoms without compromising the benefits of the medication.
At the Warwick Bowel and Hernia Clinic, we often see patients who are unsure whether their digestive symptoms are related to diet, stress, or medication. If your bowel habits change after starting a new medication, it’s worth paying attention. Small symptoms can provide important clues and addressing them early can make treatment easier and more comfortable. Book an appointment today if you are concerned about any bowel symptoms.
