I know this is an old thread, but I wanted to add to what others had said. If your doctor specifies on the rx that you take the active pills only (thus it's a 21 day rx instead of 30 day rx) insurance will cover it every three weeks.
Most insurances have a mail order or 90 day rx option, I've found this super easy, my dr faxed my rx to medco for 4 packs for a 90 days supply, so every 3 months I have a refill come in the mail-so easy and convenient once I got it set up!