When to see a doctor
Although many men can take Sildenafil and experience mild side effects or none at all, severe side effects can occur rarely. If you experience any of the following side effects while you’re taking sildenafil, you must get medical help straight away.
Severe side effects of sildenafil include severe allergic reactions (rashes; itching; hives; swelling of the mouth, face, lips or tongue; breathing difficulties; chest tightness). Other severe side effects include fast or irregular heartbeat; shortness of breath; burning sensations; chest pain; mental confusion; memory loss; passing out; tingling or numbness in arms or legs; a feeling of weakness on one side; seizure; persistent dizziness; severe or persistent nosebleeds; vision changes or loss of vision; problems speaking; hearing impairment or loss.
Sildenafil can also cause a painful erection that lasts for longer than four hours. This is known as priapism. If you experience any of these side effects, see a doctor immediately.