Q) If a lady is taking birth control pills does she still need to abstain on her yemei veses?
A) The Poskim differ as to whether a lady needs to be choshesh for her yemei veses (calculated from a natural period) when she is taking birth control pills that will withhold her menstruation. (Both Rav Wosner in Shi’urei Shevet Halevi 184:8 and the Be’er Moshe are meikel in certain circumstances.)
Important factors that will influence the final ruling include the type of birth control pill being taken, whether or not this particular lady has previously taken this pill and how she reacted to it in the past, and if the veses in question is a veses she’eino kovua, or a veses kovua (or onah beinonis).
Q) After a lady discontinues taking birth control pills what does she need to be concerned about?
A) Since it has been established that we are discussing birth control pills that withhold menstruation, it is expected and inevitable that she will menstruate after cessation of the pill. That being so, she is required to abstain and perform a bedika (as on a normal onas haveses) at the time that menstruation is expected to begin (based on her own experience with this specific birth control and/or the information leaflet that accompanies the medication). Some also require that she abstain 24 hours before she expects the menstruation to begin (Ma’re Kohen page 152).
Q) Is a period brought about by discontinuing birth control pills a reason to be choshesh for a veses in the future?
A) There is no reason to be chosesh for veses hachodesh or veses haflogo – since the period was artificially induced. However, she will need to be choshesh for onah beinonis from this period (if she does not continue the hormonal treatment) (Mar’e Kohen page 153).