Sildenafil does not prevent pregnancy or the spread of sexually transmitted diseases such as human immunodeficiency virus HIV. Storage Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Dosing The dose of this medicine will be different for different patients. The thing is, erectile dysfunction is a lot more common than people think. Tadalafil Cialis. You can take it in a small dose daily or in a larger dose as needed.Generic Viagra (sildenafil) is an alternative to the branded Viagra drug that can be used for treating erectile dysfunction (ED). It’s now sold by many manufacturers, including online. For treatment of erectile dysfunction: For oral dosage form (tablets): Adults up to 65 years of age—50 milligrams (mg) as a single dose no more than once a day, 1 hour before sexual . Viagra is a brand-name prescription drug that’s approved to treat erectile dysfunction (ED). With ED, you’re unable to have or maintain an erection. Viagra is approved for this use .