Generally there is not any effect of this medicine on men but sometimes few people feel headache, flushing, stomach upset, nasal stuffiness, diarrhea and dizziness.

If these effects persist or worsen, notify your doctor promptly. Unlikely but report promptly: painful or other urination problems, vision problems, skin rash, chest pain, fainting, foot or ankle swelling.

If you experience a painful or prolonged erection (lasting longer than 4 hours), stop using this drug and seek immediate medical supervision. If you notice other effects not listed above, contact your doctor or pharmacist.

If you take any medicines that have nitrates in them (like nitroglycerin for chest pain)—every day or even once in a while—you should NOT take VIAGRA. Discuss your general health status with your doctor to ensure that you are healthy enough to engage in sexual activity.

In rare cases, men taking PDE5 inhibitors (oral erectile dysfunction medicines, including VIAGRA) reported a sudden decrease or loss of vision. It is not possible to determine whether these events are related directly to these medicines or to other factors. If you experience sudden decrease or loss of vision, stop taking PDE5 inhibitors, including VIAGRA, and call a doctor right away.

If you are older than age 65, or have serious liver or kidney problems, your doctor may start you at the lower dose of VIAGRA. If you are taking protease inhibitors, such as for the treatment of HIV, your doctor may recommend a 25-mg dose and may limit you to a maximum single dose of 25 mg of VIAGRA in a 48-hour period.

If you are suffering from prostate problems or high blood pressure for which you take medicines called alpha blockers, your doctor may start you on a lower dose of VIAGRA.