When you take a medicine, you may think its journey begins in the stomach and ends after it reaches the part of the body where it is needed. However, that is not the entire story. Your digestive system plays an important role in how a medicine is absorbed, changed and eventually removed from the body. Dr Abhishek Deepak, Senior Consultant Gastroenterology at Fortis Greater Noida, says that the gut does much more than digest food.

"Research in gastroenterology has shown that the gut microbiome, the intestinal lining, and digestive function can all influence how well a medication works and whether it causes side effects," said Dr Deepak. This means two people taking the same medicine at the same dose may not always have the same response. One person may absorb more of the drug, while another may absorb less or experience more side effects.

Your Gut Microbiome Can Process Medicines

The intestines contain trillions of bacteria that form the gut microbiome. These microbes do more than support digestion and immunity. They can also interact with medicines and produce enzymes that change the chemical structure of some drugs. Dr Deepak explains that the microbiome can act almost like a "second liver" because bacteria can modify medicines before they reach the liver.

One example is digoxin, a medicine used for certain heart conditions. A gut bacterium called Eggerthella lenta can break down digoxin, potentially reducing the amount of active medicine available and affecting its effectiveness.

Gut bacteria can also have the opposite effect. They can reactivate some medicines and contribute to side effects. With the chemotherapy drug irinotecan, for example, bacterial activity in the intestine can reactivate a form of the drug. While this process is linked to its effects, it can also increase the risk of diarrhoea.

These differences may partly explain why the same medicine and dose can produce different results in different people.

The Intestinal Lining Affects Drug Absorption

Most medicines taken by mouth are absorbed through the small intestine. For a drug to work properly, it needs to pass through the intestinal lining and enter the bloodstream in sufficient amounts. When this lining is inflamed or damaged, absorption can become less predictable. Conditions such as inflammatory bowel disease (IBD) and celiac disease may interfere with normal absorption of some medicines.

Food and beverages can also affect how certain drugs are absorbed. For instance, taking levothyroxine with coffee can reduce its absorption. Similarly, dairy products can interact with some antibiotics and lower the amount of medicine absorbed, thereby, reducing their effectiveness.

This is why doctors and pharmacists may advise patients to take particular medicines on an empty stomach or keep them separate from certain foods and drinks.

Stomach Acid Can Change How Drugs Work

The stomach's acidity is another important factor. Some medicines need an acidic environment to dissolve and be absorbed properly. Proton pump inhibitors (PPIs), which reduce stomach acid, are commonly used to treat conditions such as acid reflux and stomach ulcers. However, reducing acidity can affect the absorption of medicines that depend on a highly acidic environment, such as ketoconazole.

This does not mean PPIs are unsafe or that patients should stop taking them. Rather, it highlights why doctors need to know about all the medicines a person is using before making changes to treatment.

Gut Movement Also Plays A Role

The speed at which food and medicines travel through the digestive tract can influence drug absorption.

Diarrhoea can move contents through the intestine too quickly, leaving less time for some medicines to be absorbed. On the other hand, constipation can slow the movement of material through the intestine and potentially prolong the time a medicine remains in contact with the gut.

The effect varies depending on the medicine, its formulation and the underlying digestive problem. Therefore, persistent diarrhoea, severe constipation or other major changes in bowel habits should be discussed with a doctor, particularly when a person is taking important long-term medicines.

The Gut Starts Processing Drugs Before The Liver

The liver is widely recognised as a major organ involved in drug metabolism, but it is not the first place where every medicine is processed. After absorption from the intestine, blood from the digestive tract travels to the liver through the portal vein. Before and during this process, the gut can already influence the medicine.

Gut enzymes and bacteria may activate a prodrug, deactivate a medicine or alter its effects. This is one reason researchers are increasingly studying the gut microbiome when trying to understand differences in medication response.

Why Gut Health Matters For Treatment

Antibiotics, probiotics, diet and gastrointestinal diseases can all change the environment in which medicines are processed. Antibiotics, for example, can alter the composition of gut bacteria, potentially changing how certain drugs interact with the microbiome. Researchers are now exploring whether a person's microbiome could eventually help doctors choose medicines or adjust doses.

"Your gut is far more than a digestive tube; it is an active partner in how medicines work. A healthy gut can influence whether a drug is stronger or weaker, acts faster or slower, and even whether it causes side effects. Understanding the gut may be one of the keys to more effective and personalized treatment," said Dr Deepak.

Disclaimer: This content including advice provides generic information only. It is in no way a substitute for a qualified medical opinion. Always consult a specialist or your own doctor for more information. NDTV does not claim responsibility for this information.