Like any medication, Actilis 20mg may cause some side effects, though most are mild and temporary. The most common side effects include headache, dizziness, flushing, nasal congestion, muscle pain, and indigestion. Some people may also experience back pain, vision changes (blurred vision or sensitivity to light), or nausea. Serious side effects are rare but may include a prolonged or painful erection (priapism), sudden vision or hearing loss, or severe chest pain. If you experience any of these serious side effects, seek immediate medical attention. To reduce the risk of side effects, take Actilis exactly as prescribed and avoid excessive alcohol consumption, as it can worsen dizziness and lower blood pressure. If side effects persist or become bothersome, consult your doctor for possible dose adjustments or alternative treatments.