GLP-1 medications and gut health: why digestion changes and how to support your gut

GLP-1 medications have been used in the UK to treat type 2 diabetes for close to two decades, but it is in weight management that they have made recent headlines, and for good reason: they can produce between 15 and 22% weight loss. With around 30% of adults in England now living with obesity, they are now widely prescribed privately, and are also available on the NHS if certain criteria are met.  An estimated 1.6 million adults in Great Britain used one to support weight loss in 2025. As such, they have the ability to transform health not only on an individual level, but on a wider population scale. 

These drugs are often well-tolerated, but side effects are common, and patients ask me: “Is it normal to feel sick?”, “Why am I constipated?”, “Is something wrong with me?”.  The reassuring answer is that these medicines act directly on your digestive system, so some change in how your gut behaves is to be expected. Here I'll explain what's normal, what isn't, and how to support your gut during your weight-loss journey. 

What are GLP-1 medications? 

GLP-1 stands for glucagon-like peptide-1, a hormone your gut releases after eating. GLP-1 medications act on GLP-1 receptors and mimic its effects, and the drugs are injected weekly or taken as a daily tablet. You may know them by brand: Ozempic, Wegovy and Rybelsus (forms of semaglutide), or Mounjaro (the dual GLP-1/GIP agonist tirzepatide). These drugs work by stimulating the pancreas to release insulin when blood sugar rises, quieten appetite signals in the brain, and slow the rate at which the stomach empties- which explains many of the side effects. 

Why can GLP-1 medications affect your gut? 

GLP-1 receptors line the digestive tract and the brain, and these medications deliberately slow the speed at which food leaves the stomach. This is part of how they keep you fuller for longer and you thus eat less. However this means food lingers, gut motility changes, and the digestive symptoms many people notice stem directly from this slowing. They're usually most pronounced when you start the medication and after each dose increase, then tend to settle as the body adapts. 

Common digestive changes people report on GLP-1 medications 

The side effects most commonly reported affect the gut, and 40–70% of people experience these: 

They're generally dose-dependent and temporary, occurring more at higher doses, which is why doses are increased slowly; for most people they settle within weeks. 

Are GLP-1 medications linked to the gut microbiome? 

Your gut microbiome is made up of trillions of microbes in your digestive tract, and GLP-1 medications and the microbiome appear to influence one another in both directions. Your microbes help set how much GLP-1 you release naturally (via short-chain fatty acids made from fibre), and the medications in turn appear to reshape the microbial community. A systematic review found they can shift it towards bacteria linked to better metabolic health, such as Akkermansia muciniphila, though findings vary, and much of the strongest data is still from animal studies. 

How appetite changes can affect gut health 

GLP-1 medications reduce appetite which is part of how they drive weight loss, but eating less often means eating less fibre- the primary fuel for a healthy microbiome. That reduction, together with slower motility, is a common driver of constipation.  Eating a varied, fibre-rich diet therefore matters more than ever on these medications. 

How to support your gut while taking a GLP-1 medication 

These tips are drawn from clinical practice recommendations, and are the ones I share with my own patients: 

Can probiotics support gut health while taking GLP-1 medications? 

Probiotics are the friendly live bacteria found in supplements and fermented foods, and the right ones taken alongside a GLP-1 medication may help in two ways. 

1. Easing the digestive side effects 

The best evidence is for constipation, where certain probiotics help you go more regularly, working to counter the slowing these medications cause. Bloating and abdominal discomfort can respond too: in a randomised trial, a multi-strain Lactobacillus formula-  the kind found in live-bacteria supplements such as Symprove- produced a significant improvement in overall IBS symptoms. The effect of any probiotic is strain-specific, so it's worth choosing a product that names its strains and has been studied in people. 

2. Complementing the metabolic effects 

Probiotics appear to work on some of the same mechanisms as GLP-1 medications, meaning they may enhance your response to treatment. Studies show probiotic supplementation can gently improve blood sugar and support modest reductions in weight and waist size.  

If you'd like to try one, use it for at least 8 weeks, and combine it with plenty of fibre and fermented foods. 

When to speak to a healthcare professional 

Most digestive symptoms on a GLP-1 medication are mild, expected and self-limiting. Speak to your prescriber or GP if you continue to have mild side effects that bother you.  

Some symptoms, however, do warrant prompt attention; seek urgent medical assistance if you experience any of the following: 

FAQs 

Do GLP-1 medications affect gut health? 

Yes. They slow stomach emptying, so digestive changes such as nausea, constipation, diarrhoea, reflux, bloating, burping are expected. Most are mild and settle with time. 

Why do GLP-1s cause constipation? 

They slow down gut motility, and combined with reduced fibre intake as appetite falls, this makes the system sluggish. Fibre, fluids and movement all help. 

Can GLP-1s cause diarrhoea? 

Yes. Diarrhoea is among the most commonly reported effects, particularly early in treatment or after a dose increase. 

Do GLP-1s change the gut microbiome? 

Emerging evidence suggests they can shift its composition, sometimes favourably, though human data remain limited. 

When should I speak to a doctor about GLP-1 digestive side effects? 

If symptoms are severe or persistent- especially severe abdominal pain, signs of dehydration, or yellowing of the skin or eyes.  Please seek medical advice promptly. 

Summary 

GLP-1 medications act mainly on your gut, so some digestive change is expected, but this is not a sign that something is wrong. Nausea, altered bowel habits and early fullness are common, especially early on and after dose changes, and usually ease as your body adapts. To support yourself: eat smaller meals with plenty of fibre, ensure good hydration, add in regular movement, and consider probiotic support. 

To learn more about this and other gut health topics, visit Symprove's Gut Hub. 

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