This medicine also works best when you take it an hour before sex on an empty stomach. Medicines that you take by mouth are called oral medicines. The generics cost much less, and—in the case of sildenafil—come in 20 mg doses. The lower dose, meanwhile, is for those who have not tolerated the higher doses well. Severe liver disease. · a light-headed feeling, like you might pass out. Common sildenafil side effects may include: flushing (warmth, redness, or tingly feeling); headache, dizziness; . 25 rows · Compare risks and benefits of common medications used for Erectile . Sildenafil oral tablet is available as a brand-name drug and as a generic drug. Brand names: Viagra, Revatio. Sildenafil comes in three forms: an oral tablet, an .