Viagra, as with all ED medications, should not be taken more than once in any 24-hour period. The pill should be taken by mouth about one hour before you have sex, according to Pfizer, the manufacturer.

No two ED medications should be taken in the same 24-hour period even if they are different medications.

Also, ED medications should not be used with any type of other ED treatments such as injections, vacuums, implants, etc.