You need to be sexually excited for it to work. Tell your doctor if any of these symptoms are severe or do not go away: headache. What side effects can this medication cause? It comes as standard tablets, chewable tablets, and as a liquid that you swallow. 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. Key facts It usually takes 30 to 60 minutes for sildenafil to work for erectile dysfunction. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine.* 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 placebo. Also, men taking VIAGRA showed an improvement in their ability to get and keep an erection versus those who took placebo. AdWith RexMD you’re saving time and money with our Viagra delivery. Get started now. Reliable E.D. meds prescribed by real doctors. Get your free & private online visit todayFree Shipping · Discreet Packaging · Real Doctors · Personalized Plan/5 (3, reviews)Site visitors: Over 10K in the past month. About sildenafil (Viagra) Sildenafil is a medicine used to treat erection problems (erectile dysfunction). Sildenafil is also sometimes used to treat pulmonary hypertension (high blood pressure in the blood vessels that supply the lungs). If you have erection problems sildenafil works by temporarily increasing blood flow to your penis when.