You can take it in a small dose daily or in a larger dose as needed. Common side effects include headache, facial flushing, indigestion, and dizziness. They’re often the first line of treatment for trouble getting or keeping an erection, called erectile dysfunction ED. You can take this medicine with or without food 30 minutes before sex, depending on the dose. This medication is taken with or without food an hour before sex.Viagra is a small, blue, easy-to-swallow tablet for erectile dysfunction. Sildenafil, the active ingredient in Viagra, works by loosening blood vessels and helping blood flow more easily to the penis. It’s a tablet you take on demand, and starts to work in minutes. Vision changes. Muscle pain. But there are some differences. With Viagra, there is a higher risk of vision changes than with Cialis. Among people who take Viagra or sildenafil, 3% get blue vision that lasts a few hours. On the other hand, Cialis has a slightly higher risk of muscle pain than Viagra and vardenafil. Generic Viagra (sildenafil): $4 per 25 mg pill, $6 per 50 mg pill, $10 per mg pill; Branded Viagra: $90 per 25 mg, 50 mg, or mg pill; Generic Cialis (tadalafil): $11 per 5 mg pill, $44 per 10 mg or 20 mg pill; Generic Cialis Daily (tadalafil): $8 per mg or 5 mg pill; Branded Cialis: $10 per 5 mg pill, $80 per 10 mg or 20 mg pill.