If a woman is expected to have a menstrual period at a time that is inconvenient or troublesome from an operational standpoint, it is often possible to postpone the menstrual flow using BCPs.

As originally designed, the progestin half of the birth control pill suppresses ovarian function, inhibiting ovulation, hormone production, and menstruation. The estrogen half of the pill serves to “add-back” a little bit of estrogen hormone to prevent low hormone side effects, such as vaginal dryness and hot flashes.

The consequence is continuous low levels of estrogen and moderate levels of progestin.

If a woman were to take those pills indefinitely, she would never get a menstrual flow, because menstrual flows are only triggered by a sudden drop in hormones, such as occurs with normal monthly cycles, or if the birth control pill were to be completely stopped. The latter occurs normally during the fourth week of a birth control pill cycle.

So from this standpoint, simply taking the birth control pill continuously, without any “off days” would be expected to postpone a menstrual period indefinitely, as long as the pills are taken every day.

That said, there are a some complexities to this:

Not all BCPs consistently suppress ovulation, particularly the newer pills containing progestins that are either not as powerful as the older progestins, or with shorter half-lives. Ovarian suppression usually works better with the older progestins, such as levonorgestrel. Levonorgestrel-containing BCPs include LoOvral, Levlen, and Portia.

Accidental skipping of BCPs during this time can lead to a relaxation of the ovarian suppression, allowing ovulation to resume and lead to a menstrual flow 2 weeks later. This is particularly troublesome with the shorter half-life progestins. The longer half-life progestins tend to be more forgiving in this area.

Depending on which pill is used and when it is started during the menstrual cycle, the woman may still experience one more menstrual period before the BCP suppression is totally effective. For this reason, it may be prudent to start the continuous BCPs at least a couple months before amenorrhea is desired, to allow the BCP time to fully suppress ovarian function.

“No menstrual period” is not the same as “no bleeding.” Many women who take BCPs continuously find that even though they no longer have regular menstrual flows, they still experience some episodes of light spotting, particularly if exercising heavily, or following intercourse.