Which Is More Effective? That means seven out of 10 people who take these drugs as prescribed will have more frequent or longer-lasting erections. If you have certain health conditions or are taking certain medications, your doctor may tell you to take sildenafil less often. Take sildenafil exactly as directed. Take sildenafil as needed before sexual activity. The most common side effects of VIAGRA: headache; flushing; upset stomach; abnormal vision, such as changes in color vision such as having a blue color tinge and blurred vision; stuffy or runny nose; back pain; muscle pain; nausea; dizziness; rash.VIAGRA may not be right for every man, but it has been shown to help approximately 4 out of 5 men get and keep erections hard enough for sex at doses of 50 mg or mg.* * Seventy-two percent, 80%, and 85% of the patients on 25 mg, 50 mg, and mg of VIAGRA, respectively, achieved erections hard enough for sex, compared to 50% on . Still, if your doctor says it’s okay for you to use and you end up paying out-of-pocket, you can still get the generic for a lot less than Viagra. According to price-comparison site test1.ru VIAGRA can cause your blood pressure to drop suddenly to an unsafe level if taken with certain other medicines. Do not take VIAGRA if you take any other medicines called “nitrates.” Nitrates are used to treat chest pain (angina). A sudden drop in blood pressure can cause you to feel dizzy, faint, or have a heart attack or stroke.