Your Gut May Change How Your Medicine Works, Gastroenterologist Explains

The digestive system can play a significant role in determining how medicines are absorbed, processed and removed from the body, according to Dr Abhishek Deepak, Senior Consultant Gastroenterology at Fortis Greater Noida. Factors including the gut microbiome, intestinal lining, stomach acidity and the speed at which food moves through the digestive tract can influence how a medicine behaves, meaning people taking the same drug and dose may experience different responses.

The trillions of bacteria that make up the gut microbiome can interact with certain medicines and produce enzymes capable of changing their chemical structure. Dr Deepak explained that these microbes can function in some ways like a "second liver", modifying medicines before or as they reach the liver. For example, Eggerthella lenta, a gut bacterium, can break down digoxin, potentially reducing the amount of active medicine available. Gut bacteria can also reactivate certain drugs and contribute to side effects, as seen with irinotecan and its association with diarrhoea.

The intestinal lining is another important factor because most medicines taken orally are absorbed through the small intestine before entering the bloodstream. Inflammation or damage caused by conditions such as inflammatory bowel disease or celiac disease can make absorption less predictable. Food and beverages can also interfere with certain medicines. Levothyroxine, for instance, can be absorbed less effectively when taken with coffee, while dairy products can interfere with the absorption of some antibiotics.

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Stomach acidity can also affect how certain medicines dissolve and enter the bloodstream. Some drugs require an acidic environment for proper absorption, while medicines such as proton pump inhibitors reduce stomach acid and may therefore influence the absorption of drugs that depend on high acidity, including ketoconazole. This does not mean patients should stop prescribed medicines, but it underlines the importance of informing doctors and pharmacists about all medications being taken before treatment is changed.

The movement of food and medicines through the digestive tract can further influence absorption. Diarrhoea may speed up intestinal movement and leave less time for some medicines to be absorbed, while constipation can slow transit and potentially prolong contact with the intestinal tract. The impact varies according to the medicine and its formulation, so persistent diarrhoea, significant constipation or major changes in bowel habits should be discussed with a doctor, particularly when taking important long-term medication.

Researchers are increasingly examining the gut's role in personalised medicine, including how antibiotics, diet, probiotics and gastrointestinal conditions can alter the microbiome and potentially change drug responses. Dr Deepak emphasised that the gut is an active participant in medication processing rather than simply a digestive passage, and understanding these interactions could eventually help doctors select treatments and adjust doses more precisely for individual patients.

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