viagra online

Sildenafil, sold as the brand name Viagra among others, is a medication used to treat erectile dysfunction and pulmonary arterial hypertension. Its is unclear if it is effective for treating sexual dysfunction in women. It is taken by mouth or injection into a vein. Onset is typically within 20 minutes and lasts for about 2 hours.Common side effects include headaches, heartburn, and flushed skin. Caution is advised in those with cardiovascular disease. Rare but serious side effects include a prolonged erection that can lead to damage to the penis, vision problems, and hearing loss. Sildenafil should not be taken by people on nitrates such as nitroglycerin (glycerin trinitrate), as this may result in a serious drop in blood pressure.Sildenafil acts by blocking phosphodiesterase 5 (PDE5), an enzyme that promotes breakdown of cGMP, which regulates blood flow in the penis. It requires sexual arousal, however, to work. It also results in dilation of the blood vessels in the lungs.Pfizer originally discovered the medication in 1989 while looking for a treatment for heart related chest pain. It was approved for medical use in the United States and Europe in 1998. In the United States about 2 million prescriptions were written for sildenafil in 2016. In 2017 it became avaliable as a generic medication. In the United Kingdom it is avaliable over the counter. As of 2018 in the United States the wholesale cost is less than 1 USD per dose.

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