Tadalafil 20 mg is a widely used medication, and while it is generally well-tolerated, some mild side effects can occur. The most common ones include headaches, indigestion, back pain, muscle aches, facial flushing, and a stuffy or runny nose. These symptoms are usually temporary and subside on their own. Less common but important side effects include sudden vision or hearing changes, or an erection lasting more than four hours. If you experience any severe symptoms, please seek prompt medical advice. Always consult your doctor before starting, especially if you take nitrate medications for heart conditions.