Scars on penis, painful and long erection, any kidneys diseases, crescent-cellular anaemia, liver diseases, blood disease, cancer, leucaemia, eye diseases, such as diseases of retina or pigmentary retinitis, gastric ulcer, heart disorders, such as heart attacks or serious arrhythmia within the last 6 months, impaired cardial function, coronary disease with unstable angina, recent stroke within the last 6 months, very high or low level of blood pressure.

This drug can cause temporal loss of color perception. Be careful at activity demanding coordination, such, for example, as driving car or working with mechanisms. To reduce to minimum dizziness, stand up slowly from sitting or lying position.