Viagra (sildenafil) is a drug that can be prescribed to treat erectile dysfunction, also commonly known under the name of male impotence. It works in 80% of all cases providing for long-lasting hard erections. Viagra is not supposed to be taken along with alcohol, grapefruit juice or in combination with nitrate-based drugs. The last factor can lead to a sudden drop in blood pressure that may result in fainting, stroke or heart attack. Be very careful when you start taking any new medications and always ask your doctor or your pharmacist if you are not sure whether they can interact with Viagra or not. Other medicines that have also been reported to cause interference include, but are not limited to: alpha blockers, other erectile dysfunction medications, efavirenz, medications for high blood pressure, antifungals, anticoagulants, HIV protease inhibitors, rifampin, barbiturates, cimetidine, rifabutin, beta blockers, medications for seizures, and erythromycin. Your dose of Viagra will depend on the severity of your impotence and a number of other factors. For example, older patients may need a lower dose of this medicine, as the effects of Viagra can be stronger for them. Older patients need to be careful with taking Viagra at any doses, as age (being older than 50) is one of the risk factors for developing sudden vision loss. This serious health condition is caused by reduced blood flow to the optic nerve of the eye and besides your age can be contributed to by such factors as your habits (smoking) and some medical problems you have (high blood pressure, a history of a heart attack and high cholesterol levels). Discussing all the risks and benefits of the treatment is recommended if you have any of the risk factors mentioned. Some mild side effects are possible if you take Viagra, even if you take it exactly as prescribed. In most case these side effects just mean your body needs time to adjust to the dose prescribed, and they are likely to go away on their own without any need for you or your doctor to interfere. The following mild side effects are most likely: heartburn, numbness, burning, or tingling, headache, muscle aches, diarrhea, insomnia, light sensitivity, flushing, and nosebleeds. Never share your dose of Viagra with anyone else, as you may not know if this person has any contraindications and whether the treatment will be completely safe for them.