Natural Viagra alternative without a prescription.
Some medicines can cause unwanted or dangerous effects when used with Viagra. Tell your doctor about all your current medicines, especially riociguat (Adempas).
Do not take Viagra if you are also using a nitrate drug for chest pain or heart problems, including nitroglycerin, isosorbide dinitrate, isosorbide mononitrate, and some recreational drugs such as "poppers". Taking sildenafil with a nitrate medicine can cause a sudden and serious decrease in blood pressure.
Contact your doctor or seek emergency medical attention if your erection is painful or lasts longer than 4 hours. A prolonged erection (priapism) can damage the penis.
Stop using Viagra and get emergency medical help if you have sudden vision loss.