The best time to take sildenafil is about 1 hour before sexual activity, but you can take the medication any time from 4 hours to 30 minutes before sexual activity. Contact your medical provider if you experience any side effects during treatment. How should this medicine be used? Cialis stays in your system for up to 36 hours, and you can take it daily. Cialis Daily tadalafil : This low-dose Cialis works by increasing blood flow to the penis over time, making it easier to have an erection when aroused.Brand names for sildenafil include Viagra, Revatio, and Liqrev. The cost for sildenafil oral tablet mg is around $10 for a supply of 2 tablets, depending on the pharmacy you . 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. Generic Name(S): sildenafil. Uses; Side Effects; Precautions; Interactions; Overdose; Images; Reviews () Uses. Sildenafil is used to treat male sexual function problems (impotence or erectile.