西地那非（英语：Sildenafil），又译昔多芬，是一种研发治疗心血管疾病药物时意外发明出的治疗男性勃起功能药物。法律规范为处方药品，需医生诊断后开立处方笺才可购得服用。 一般以其商业用名Viagra（中国大陆注册名万艾可，台湾和港澳商品名威而钢）广为人知，在大陆和香港俗称“伟哥”、在台湾则俗称“蓝色小药丸”。目前瑞辉制药对西地那非的专利权已过期，其他厂商可以合法制造同种药物。伟哥和希爱力谁更好？ 阿伐那非（Stendra）还是伟哥（Viagra）？不引起副作用、效果好、方便使用的药物就是最适合治疗ED 的药。 有些男性根据性生活习惯和频率选择按需服用药物，如在性行为前服用伟哥（Viagra）、希爱力（Cialis）或艾力达（Levitra）等。 对于其他计划性不强的男性，则更倾向于每天服用，不管是否计划要进行性生活都可随时起效。 在正确使用药物，并且药物剂量是通过纽约泌尿专家中心（New York Urology Specialists）调整好的情况下，所有药物都能发挥同等的效果，不过有些男性对一些药物的反应会比其他药物更强。 通常这只能通过不断尝试来确定. Sildenafil, sold under the brand name Viagra, among others, is a medication used to treat erectile dysfunction and pulmonary arterial hypertension but Viagra typically starts to work between 30 and 60 minutes after you take a dose of the drugbut Viagra itself doesn’t give you an erection. You’ll need to be sexually aroused in order for the drug to work.Viagra keeps working in your body for up to 5 hours.This means that if you’re aroused, you should still be able to get an erection up to 4 hours after taking a dose of Viagra.Even though Viagra keeps working in your body for several hours, your erection shouldn’t last this long. In fact, in rare cases, Viagra can cause priapism (a long-lasting and sometimes painful erection).Priapism is a medical emergency that needs to be treated right away. If it’s not treated, the condition can damage the tissues in your penis and cause irreversible erectile dysfunction.When you’re sexually aroused, your brain sends messages to your penis.These messages cause certain chemicals to be released in your penis.One of these chemicals, called cyclic GMP, relaxes and widens certain blood vessels in your penis. Cyclic GMP also relaxes the muscles around the erectile tissue in your penis that’s called the corpus cavernosum.These actions allow blood to flow into the corpus cavernosum, which causes your penis to get hard and become erect.ED can occur if you have certain problems that affect your body’s ability to have an erection.The condition can result from problems with messages being sent from your brain. ED can also result from problems with blood flow into your penis.
