The most common side effects are gastrointestinal. Because semaglutide slows digestion and reduces appetite, nausea is frequently reported, especially when first starting or increasing the dose. Some people also experience vomiting, diarrhea, constipation, or heartburn. Usually these effects are mild-to-moderate and improve over time as the body adjusts. Other possible side effects include headache, fatigue, or slight increases in heart rate. A rare but serious side effect (observed in this drug class) is a type of thyroid tumor in rodents, but it has not been seen in humans – nonetheless, semaglutide isn’t given to people with a history of certain thyroid cancers as a precaution. It’s important to note that any medication that causes rapid weight loss can also carry risk of gallstones. In practice, patients are monitored and side effects are managed by dose adjustments.