Immediately seek medical help if you experience:

• chest pain
• an allergic reaction: difficulty swallowing or breathing, shortness of breath, wheezing, fever, skin rash, hives, swelling
• a painful erection of the penis lasting longer than 4 hours in duration
• sudden decrease or loss of hearing
• a sudden decrease or loss of vision
• temporary memory loss
• seizure

Other possible side effects

• headache
• muscle pain
• facial flushing
• nausea
• pain in the arms or legs
• back pain
• upset stomach or heartburn
• diarrhea
• flu-like symptoms
• difficulty sleeping
• cough
• nosebleed

Sildenafil helps the blood vessels in the lungs relax. This allows more blood to flow into your lungs and reduces the blood pressure in the arteries of your lungs.

Do not take sildenafil if you:

• are taking any medications that contain nitrates, which are used for chest pain; if you are not sure, check with your pharmacist
• are taking any medications that are guanylate cyclase stimulators, such as riociguat
• have had an eye disease called non- arteritic anterior ischemic optic neuropathy (NAION)
• have pulmonary veno-occlusive disease (PVOD)
• are allergic to any part of it

Use sildenafil with caution in:

• heart disease or previous heart attack or stroke
• low blood pressure or uncontrolled high blood pressure
• liver problems
• kidney problems
• sickle cell anemia
• multiple myeloma, leukemia
• stomach ulcers or bleeding problems
• retinitis pigmentosa

Avoid the following medications while on sildenafil:

• nitrates, including nitroglycerin, isosorbide mononitrate, isosorbide dinitrate
• verapamil or diltiazem
• some antibiotic medications such as rifampicin, erythromycin, clarithromycin, telithromycin
• some antifungal medications such as ketoconazole, itraconazole
• some medications used to treat HIV such as ritonavir, saquinavir
• some antiseizure medications such as phenytoin, carbamazepine, phenobarbital
• other medications used to treat PAH including bosentan
• other similar medications, including tadalafil and vardenafil
• St. John’s Wort

Discuss with your doctor if you are taking:

• medications to lower your blood pressure
• doxazosin or other "alpha blockers"

Do not take/consume products containing grapefruit as they can increase the effects of this medication. 

Use in pregnancy: information is limited but there is nothing to suggest sildenafil causes defects or problems in a fetus.

Use in breastfeeding: It is unlikely that sildenafil passes into the breastmilk or causes harm to a breastfed baby. Talk to your doctor or pharmacist.