Common side effects of tirzepatide include nausea, vomiting, diarrhea, constipation, abdominal pain, decreased appetite, injection site reactions (such as redness, swelling, or pain), fatigue, and gastrointestinal issues like heartburn, gas, and bloating. Serious side effects, although less common, can include thyroid tumors, pancreatitis, and severe allergic reactions. Always consult your healthcare provider for personalized advice and to report any side effects.