GI Side Effects: Why Medicines Upset Your Stomach and What to Do

Got nausea, diarrhea, or belly pain after starting a medicine? You're not alone. Many drugs irritate the gut, change your gut bacteria, or alter digestion. Knowing which medicines are likely culprits and simple fixes can keep you comfortable and help you avoid complications.

Which drugs usually cause GI problems?

Antibiotics (like cephalosporins such as Keflex and others) often cause diarrhea or loose stools because they kill good gut bacteria. Steroids (for example, prednisolone) can cause stomach pain, indigestion, or bloating, especially if taken without food. Antidepressants such as SSRIs (Prozac/fluoxetine) commonly cause nausea or changes in bowel habits when you first start them. Some anti-inflammatories and pain meds irritate the stomach lining and may cause upset or even bleeding if used long-term. Certain older or specialty antibiotics and drugs (chloramphenicol, dapsone, sulfasalazine/Azulfidine) can also bring GI symptoms—watch for persistent nausea, appetite loss, or new abdominal pain. For vomiting, studies show oral ondansetron usually works better than domperidone in acute gastroenteritis in children, so anti-nausea choice matters.

Practical steps to reduce or treat GI side effects

First, try simple changes: take the medicine with a small meal or snack if the label allows. Avoid alcohol and spicy foods while your stomach adjusts. Stay hydrated—drink water or oral rehydration solutions if you have diarrhea or vomiting. For antibiotic-related diarrhea, consider a probiotic during and after the course (ask your pharmacist which strain and timing). If nausea is the main issue, eat bland, small meals and try ginger or peppermint—both can help mild nausea.

Over-the-counter options can help but use them carefully. Loperamide can control acute diarrhea but don’t use it if you have a high fever or bloody stool—get medical help instead. Antacids or acid reducers relieve heartburn or reflux from some meds. For persistent nausea, an antiemetic like ondansetron may be prescribed by your doctor.

Always check for interactions. Some OTC drugs or supplements change how a prescription works and can worsen side effects—ask your pharmacist if you take other meds (the imipramine article shows how OTC antihistamines or decongestants can cause serious interactions). If the side effect is mild, your doctor may lower the dose or switch you to an alternative that’s easier on the stomach.

Call your doctor right away if you have severe abdominal pain, black or bloody stools, high fever, signs of dehydration, yellowing of the skin, or a sudden severe allergic reaction. For anything persistent or worrying, contact your prescriber or pharmacist. Small fixes often work, but safety comes first.

Want tailored advice? Bring a list of your meds to your pharmacist or doctor. They can point out likely offenders, safer alternatives, and straightforward ways to feel better fast.