Statins do not appear to harm your gut bacteria. The largest study so far found that people taking a statin were less likely to carry a pattern of gut bacteria linked with inflammation. Statins can still cause digestive side effects, including indigestion, constipation, diarrhoea and wind, and these usually settle in the first few weeks. If your gut is troubling you, speak to your GP or pharmacist rather than stopping a medicine that protects your heart. This guide covers what statins do to your gut bacteria, whether your symptoms are connected, and what you can do day to day.
Do statins change your gut bacteria?
A statin does not clear out gut bacteria the way an antibiotic does. Antibiotics kill gut bacteria directly, and the fall in their numbers and variety is large and fast. That is why we cover how a course of antibiotics changes gut bacteria as its own guide. Any effect a statin has is smaller and slower.
The biggest study so far was published in Nature in 2020. Researchers compared the gut bacteria of European adults taking statins with similar adults who were not. People taking a statin were less likely to carry a pattern of gut bacteria linked with higher inflammation in the body. The difference was clearest in people with obesity, where that pattern is most common.
Everyone in the study was measured once, and nobody was randomly assigned to take a statin. That means the study cannot prove the statin caused the difference. The researchers said the finding needs a proper trial before statins are treated as a way of changing gut bacteria.
Statins may also act on gut bacteria directly. A laboratory study tested over a thousand everyday medicines against common gut bacteria, and many of them, statins included, slowed the growth of some species. That happened in a laboratory, not in people. The amount of statin reaching the large intestine may be too small to do the same inside the body, and no study has shown it in patients.
Most of this research also treats statins as a single group. A 2025 review points out that they are not interchangeable. Different statins are absorbed differently, so different amounts reach the lower gut, and a finding for one may not hold for another.
Why would a cholesterol medicine affect your gut?
Statins such as atorvastatin, simvastatin, rosuvastatin and pravastatin work in the liver. They block an enzyme called HMG-CoA reductase, which the body uses to make cholesterol. The liver makes less, takes more cholesterol out of the blood, and LDL cholesterol falls.
Two things connect that to the gut. First, not all of each tablet is absorbed, so a small amount of the drug carries on into the large intestine, where most gut bacteria live. Second, the body makes bile acids from cholesterol. Gut bacteria feed on bile acids and alter them chemically, so a medicine that changes how the body handles cholesterol can reach the bacteria through the bile acids as well.
Statins are one of the everyday medicines researchers have looked at most closely for gut effects, alongside acid-reducing medicines, metformin and anti-inflammatory painkillers. A 2021 review of that research concluded that broad patterns can be described, but that no medicine yet has a reliable bacterial fingerprint. We cover two of the other groups in our guides to how proton pump inhibitors affect the gut microbiome and what NSAIDs do to the gut lining and gut bacteria.
Can statins cause indigestion and other gut symptoms?
Yes. The NHS lists constipation, diarrhoea, wind, feeling sick and indigestion among the possible side effects of statins. These symptoms are usually mild. They tend to start in the first weeks of treatment or after a dose change, and they often settle on their own.
Whether the statin is really the cause is difficult to judge. In a trial run through GP practices in England and Wales, people who had stopped a statin because of muscle pain took their statin and an identical placebo in alternating periods. They did not know which was which. On average their symptoms were no worse on the statin than on the placebo, and two thirds chose to restart a statin afterwards. That trial looked at muscle symptoms, and nobody has run one like it for gut symptoms. It still shows how hard it is to tell from experience alone whether a daily tablet is causing a symptom.
If you think your statin is upsetting your gut, tell your GP or pharmacist. They can look at the timing, check your other medicines, and consider whether a different statin, a lower dose or a different schedule would help. Never stop a statin on your own, because it was prescribed to lower your risk of a heart attack or stroke.
Do your gut bacteria change how well your statin works?
People respond to statins differently. Two people on the same dose can end up with quite different cholesterol results, and genetics explains only part of the gap. Researchers have asked whether gut bacteria explain some of the rest.
In two large groups of American adults, the mix of bacteria in a person's gut was linked with how strongly they responded to their statin. That covered the intended effect on cholesterol and the unwanted effect on blood sugar control.
This is an association, not proof of cause. No gut test exists yet that a GP could use to guide statin prescribing. The researchers themselves say more work is needed first.
The idea is taken seriously because of what gut bacteria can do to medicines. A 2025 review from the School of Pharmacy at Queen's University Belfast describes how bacteria can chemically alter a drug, switch it off, or absorb it into their own cells before it reaches its target. For now this is research, not something that changes anyone's prescription.
Statins, blood sugar and gut bacteria
Statins slightly raise the chance of developing type 2 diabetes in some people. This is already known and appears in the prescribing information. For people at meaningful risk of heart disease, the protection against heart attacks and strokes is judged to outweigh it.
Gut bacteria may be part of the reason it happens. A small 2024 study followed patients through their first months on atorvastatin and found changes in their gut bacteria and their bile acids. Later experiments linked those changes to poorer blood sugar control.
The study was small, and most of the follow-up work was done in animals. Nothing here has been repeated in a large group of people. It is a lead researchers are following, not a reason to change anything or to start a supplement. If you are worried about your blood sugar while taking a statin, ask your GP. They already monitor it and can tell you what your own results show.
Can a gut microbiome test show what a statin has done?
Not directly. If you have been taking a statin for years, there is no earlier result to compare against. A stool test also says nothing about your cholesterol or whether your statin is working, because those questions are answered by a blood test at your surgery.
What a stool test does show is the mix of bacteria living in your gut right now. A gut microbiome test measures which bacteria are present and in what proportions from one sample taken at home. That includes the overall variety of species, which is the measure that appears most often in the statin research. It also includes the levels of the fibre-fermenting bacteria that produce butyrate, the compound that feeds the cells lining your colon. Our page on what a gut diversity test can show explains how variety is reported.
A result is a snapshot of one moment. It cannot say whether a medicine caused what it finds, it never justifies changing a prescription, and it does not diagnose any condition. It can give you something specific to discuss with your GP or pharmacist. If your gut has felt unsettled for a long time, our guide to what an imbalance in your gut bacteria looks like covers the wider picture.
What can you do to support your gut while taking a statin?
Keep taking the statin as prescribed. Everything below sits alongside it, not instead of it.
- Eat plenty of soluble fibre. Oats, beans, lentils and fruit contain the kind of fibre that binds bile acids in the gut, which has a modest cholesterol-lowering effect of its own. The same fibre feeds gut bacteria, so one food choice does two jobs.
- Aim for a wide range of plant foods. Variety in your diet is the most reliable way to support variety in your gut bacteria. Our guide to which foods support gut health has the detail.
- Fermented foods such as live yoghurt, kefir and kimchi add live cultures. The evidence for them in general gut health is reasonable, though none of it comes from people taking statins. We explain the difference between probiotics and prebiotics separately.
- Check grapefruit with your pharmacist. Grapefruit and grapefruit juice slow the body's clearance of some statins, simvastatin in particular, which can raise the amount in your blood.
- Be careful with red yeast rice. It contains a compound closely related to prescription statins, so it should not be added to a statin without advice. Mention it, and any other supplement, to your pharmacist first.
Gut bacteria may even influence cholesterol on their own. Analysing samples from a long-running American heart study, researchers found that people carrying more of one particular group of gut bacteria had lower cholesterol. In the laboratory, those bacteria broke cholesterol down themselves. This is early research. There is no way to take these bacteria on purpose, and it does not mean a diet change can replace a statin.
When should you see a GP or pharmacist?
Two warning signs belong to statins specifically. Unexplained muscle pain, tenderness or weakness needs same-day advice, especially if you also have dark urine or a fever, because very rarely a statin can trigger serious muscle breakdown. Yellowing of your skin or the whites of your eyes, or dark urine with pale stools, can point to a liver problem and needs a prompt review too.
Some gut symptoms need a GP appointment whoever you are and whatever you take. Book one, or call NHS 111 when the surgery is closed, for:
- Blood in your stool, or stools that are black and tarry
- A change in your bowel habit that has lasted more than three weeks
- Weight loss you cannot explain
- Difficulty swallowing, or persistent vomiting
- Stomach pain that is severe, persistent, or wakes you at night
- Feeling unusually breathless, tired or pale, which can be a sign of anaemia
- Any new digestive symptom starting over the age of 50, or alongside a family history of bowel or ovarian cancer
Severe sudden stomach pain, vomiting blood, or a rash, wheezing or swelling of the face or throat need emergency care. Call 999 or go to A&E rather than waiting for an appointment. For anything less urgent, your GP or pharmacist can look at the dose, the timing or a different statin with you. Never stop taking one on your own.
This guide is for information only and does not replace medical advice. Speak to your GP or pharmacist about your own treatment.
Sources
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