There is no single best medicine for gastrointestinal problems, as treatment depends on the underlying cause, such as acidity, infection, constipation, diarrhoea, or indigestion. Commonly used medicines include antacids or proton pump inhibitors for acidity and indigestion, antiemetics for vomiting, laxatives for constipation, and antispasmodics for abdominal cramps. Oral rehydration solution and probiotics may also help in cases of diarrhoea or imbalance of gut bacteria. It is best to consult a doctor for a proper diagnosis before starting any medication.