When choosing one, tell your doctor or other health care professional what your preferences are, such as cost, ease of use, how long the drug’s effects last and side effects. As with sildenafil, a high-fat meal or alcohol keep the body from absorbing it as quickly. How oral medicines differ Each oral medicine for ED has a slightly different chemical makeup. Sildenafil usually should not be taken more than once every 24 hours. Severe liver disease.In most males,* Viagra works within 1 hour after it’s taken. It’s possible that Viagra can begin working within 30 minutes of being taken. But other times, it may take up to 4 hours to start.  · Teva’s version of sildenafil debuted at an average cash price of around $30 per pill, roughly 50% cheaper than brand-name Viagra. Since then, more manufacturers have brought generic versions of Viagra to market, bringing prices down even further. According to price-comparison site , generic Revatio will cost you as little as $ per pill, depending on where you fill your prescription. That’s compared with .