Common side effects (affecting up to 1 in 10 people) are: headache, back or muscle pain, pain in the arms or the legs, hot flushing in the face, blocked nose and digestion problems.
Uncommon side effects (that occur in up to 1 in 100 people) include: feeling dizzy, stomach ache, nausea, vomiting, reflux, blurred vision, pain in the eye, breathing problems, blood in the urine, prolonged erection, palpitations, increased heart rate, high or low blood pressure, bleeding from the nose, tinnitus, swollen hands, feet or ankles, and tiredness.
Rare side effects (occurring in up to 1 in 1,000 people) are: loss of consciousness, seizures, short term memory loss, swollen eyelids, red eye, sudden loss of hearing, hives, bleeding from the penis, blood in the semen, increased perspiration, heart attack or stroke in men who already had a history of heart problems, patrial, temporary or permanent reduction in or loss of vision, migraines, swollen face, severe allergic reaction, disorders interfering with blood flow to the eyes, irregular heartbeat, angina, and sudden death from a cardiac event.