Which Works Faster? Cialis stays in your system for up to 36 hours and may provide support for erections during that entire time. Common ones include: Flushing of the skin. They are PDE5 inhibitors that allow for increased blood flow to the penis, leading to more frequent and harder erections. It comes as standard tablets, chewable tablets, and as a liquid that you swallow. 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. You can take it up to 4 hours before you want to have sex.Viagra (sildenafil) is a brand-name prescription drug that’s used to treat erectile dysfunction (ED). Learn about side effects, warnings, dosage, and more.  · 10 tips to use sildenafil (aka Viagra) effectively. A set of instructions should be given to patients on sildenafil: A minimum wait of 45 minutes to 1 hour is required between taking the tablet. Compare prices and print coupons for Sildenafil (Generic Revatio and Viagra) and other drugs at CVS, Walgreens, and other pharmacies. Prices start at $