Side Effects : Like all prescription medications, Scilla (Sildenafil) may cause some side effects. With Scilla (Sildenafil), the most common side effects are headache, facial flushing, and upset stomach. In extremely rare cases, Scilla (Sildenafil) can cause blurred vision or sensitivity to light. Remember, Scilla (Sildenafil) side effects are temporary and usually go away within the first few hours of use. In the rare event of an erection lasting longer than 4 hours, seek medical help.