The dose of CIALIS for use as needed should be limited to 10 mg no more than once every 72 hours in patients taking potent inhibitors of CYP3A4 such as ritonavir, ketoconazole, and itraconazole [see Drug Interactions 7. Viagra can be taken as long as four hours or as little as 30 minutes before sex. It works best when taken one hour before sex. Four strengths of almond-shaped tablets are available in different sizes and different shades of yellow: 2. In some patients, concomitant use of these two drug classes can lower blood pressure significantly [see Drug Interactions 7. You can take Viagra daily, but because the medication stays in your system for four to six hours, it will not be effective all day.The recommended starting dose for Cialis intended for once daily use is mg, take at the same time each day, without regard to timing of sexual activity. This may be increased to 5mg/day based on need and tolerability. May be taken with or without food. Cialis is available as a generic, under the name tadalafil. 3. Compare prices and print coupons for Cialis (Tadalafil (Cialis)) and other drugs at CVS, Walgreens, and other pharmacies. Prices start at $ Tablet No data Dosage mg 5mg 10mg 20mg No data Quantity 5 6 10 15 30 90 No data.