If a woman is using birth control pills (after consulting with a rabbi) with a longer-than-one-month cycle, when are her onot perisha? For example, suppose the woman becomes nidda every 3 or 4 months; does she still observe the onot perisha for the day of the month, or the 30 days? What other things must be considered in such a situation?

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    I'm not sure this can be answered without close consultation with a competent rabbi.
    – Seth J
    Sep 5, 2012 at 15:52
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    Mark, welcome to Mi Yodeya, and thanks for the interesting question. Please bear in mind that this site makes no guarantee of validity, and does not offer professional (particularly rabbinic) advice: treat information from this site like it came from a crowd of your friends, and consult an halachic authority if the question is practical for you. I hope you stick around and enjoy the site.
    – msh210
    Sep 5, 2012 at 15:53
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    Another aspect that must be considered is whether there exists a "causative onah"; e.g., if the period always begins 3 days after stopping the active pills, that would probably have the status of an onah whenever those conditions are present.
    – Dave
    Sep 5, 2012 at 16:33
  • @Dave ...especially when that cause is a non-cause, ie not taking the pill. There is no active action.
    – Double AA
    Sep 5, 2012 at 16:41
  • related judaism.stackexchange.com/questions/17075/…
    – Double AA
    Sep 5, 2012 at 17:11

3 Answers 3


In Torat HaTahara 2:14, R' David Yosef rules "A woman who takes pills to push off her period [i.e. so that it's longer than veset ha'haflagah or veset hachodesh she established from previous periods], min hadin her husband doesn't need to separate from her at the the time of her (previously) expected veset, because in our days it's proven beyond all doubt that these pills actually do push off her period. But someone who is machmir should be blessed."

R' Mordechai Eliyahu addresses this question in detail at the end of chapter 7 of his sefer Darchei Tahorah. I'm not going to quote him in detail because it's long. In short: she doesn't need to be concerned about her old period, and she needs to be separate starting 3 days after she stops taking the pills until 7 days after she stops taking the pills (temporarily), though she can establish a veset kavua based on the number of days after she stops taking the pills, and then she only needs to separate then. He discusses in detail what happens when she stops the regimen of pills completely, and other situations related to pills.


If a woman has no set time of the month but her period always occurs more than x amount of days after her previous period, then for that amount of days she is considered to be awaiting a veset kavu'a - a regular cycle, and she need not observe any days of separation during that time. This is known as the veset of the Terumas Hadeshen, and is mentioned in Shulchan Aruch YD 186:3.* (That one who has a regular cycle need not observe any days of separation in between is found in 184:1.)

The definition of 'always' is the just like every veset; three consecutive times Halachically defines a regular cycle.

*See Pischei Teshuva 187:26 who mentions this particular application of the Terumas Hadeshen's veset, and cites the Chavos Da'as who also says so. See also the Sidrei Tahara 184:4 who mentions it in passing.

  • So if it is a 4-month cycle, it takes a year to establish veset kavua, right? In the mean time, does she observe the day of the month 3 times per cycle or only after the first month of each cycle?
    – Mark
    Sep 5, 2012 at 20:02
  • Dov, I think that is referring to the couple checking themselves. Eg. they need not check prior to 14 days. Regarding separation diring the onah, I think there is a similar concept that is disputed in the achronim. I'll have to dig up a source later.
    – YDK
    Sep 5, 2012 at 21:31
  • @YDK See my edit.
    – Dov F
    Sep 6, 2012 at 13:22
  • He must mean that the chavod daas would say that the terumas hadeshen applies it here as well (as opposed to those who only apply the terumas hadeshen to bedikos). But the chavos daas himself (186:3) argues on the terumas hadeshen's entire idea.
    – YDK
    Sep 6, 2012 at 18:55

According to R' D. Feinstein (I heard personally), predictions of what the pill will do are irrelevant. The law goes by when menstruation happens or doesn't happen. [This psak was not regarding multiple months, but a "28 day" pill. There is no 28th day onah because "How do you know?"]

So until there is a basis (chazaka) otherwise, she must keep that date of the next month.

Obviously, once the 30-day general interval passes or her personal interval from the last incidence, you don't need to worry about those anymore (there is no 60-day interval).

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    "until 3 of those dates go by without incidence" - are you referring to a case where there was a preexisting veset kavua? Otherwise I can't figure out what you mean.
    – Dave
    Sep 5, 2012 at 19:18
  • In the second month after the previous period, must she observe the day of the month?
    – Mark
    Sep 5, 2012 at 20:00
  • @Dave, actually, I originally thought that was so even by an aino kavua, but acc. to Taz 189:20, anything not kavua becomes undone with 1 opposing incident.
    – YDK
    Sep 5, 2012 at 21:15
  • @Mark, see my comment above.
    – YDK
    Sep 5, 2012 at 21:20

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