The Effectiveness of 'The Pill'??
November 3, 2016 7:09 PM   Subscribe

Why is the combination birth control pill effective after only 7 days? How do birth control manufacturers determine that this is the amount of time after which bc pills are effective? Speaking of, how much time (hours?) does it take for the bc pill to get in the blood stream after taking it.

I've tried to google this, but not much luck. I would like answers with as much nitty gritty detail as possible (graphs and numbers are great!)
posted by twill to Science & Nature (11 answers total) 2 users marked this as a favorite
I'm pretty sure it's only considered effective after 7 days if you start taking it on day 1 of your cycle (the first day of bleeding). If you start taking it mid-cycle it's best to not consider it effective until a whole pack of pills has been taken.
posted by kinddieserzeit at 7:21 PM on November 3, 2016

Just to clarify, most combination birth control pills (ie. tri-cyclen lo) claim to be effective after 7 days as per package insert on either a 'day 1' start or on a 'Sunday start'
posted by twill at 7:51 PM on November 3, 2016

I don't have specific cites, but the pill works by preventing ovulation*. If you start the pill right around your period (day 1 or Sunday), you are theoretically at least 10 days off from ovulation, and their studies (all the hoops they had to jump for FDA approval) show that 7 days taking the medication per recommended guidelines is enough time to suppress ovulation.

They know this generally from animal studies followed by human trials.

"In the bloodstream" is a complicated question. Literally entering the bloodstream should happen as a function of digestion, so 40-90 minutes maybe, but clinically effective is going to be further out than that since it requires reaching therapeutic levels before it is sufficient to disrupt ovulation (less than 7 days, though).

*Or it may be more complicated than that. Nobody actually knows. That's one of the fun things of being a woman.
posted by Lyn Never at 8:09 PM on November 3, 2016 [4 favorites]

Depending on the specific pill, it might work in more than one way. My doctor said the mini pill I'm on works by a. Suppressing ovulation, b. Thickening mucus around the cervix, which make sure it harder for sperm to get through, and c. Thinning the uterus walls so they are less able to support the implantation of an embryo. He said that b works pretty quickly and may be effective even in months where ovulation occurs due to e.g. me forgettting to take the pill every day or other reasons. They aren't such foolproof methods as the ovulation prevention, of course, but they still decrease the likelihood of a pregnancy.
posted by lollusc at 8:51 PM on November 3, 2016 [1 favorite]

I think the hormone uptake is actually pretty quick, when I've had to take the morning after pill, I noticed the side effects in a matter of hours. The section about Adverse Effects from this article on emergency contraception is interesting, in discussing whether not puking-as-a-side-effect is a concern regarding effectiveness,
" seems reasonable to infer that if gastrointestinal symptoms are estrogen-mediated secondary to an effect on the central nervous system, absorption of the dose should have occurred by the time of emesis."
With regular birth control pills, it will take some time to build up to the point where it's effective. How long is going to vary from person to person, part of that 7 days is going to be buffer for that and in case you ovulated right as you started taking the pill.

I quickly googled birth control hormone absorption and yeah, that's a mess to wade through. I don't have the time to dig further myself but if you're looking for scholarly articles I think looking up emergency contraception would be more fruitful than regular BCP, since with the morning after pill, it's that ramping-up period that's the most interesting.
posted by yeahlikethat at 8:58 PM on November 3, 2016 [1 favorite]

40-90 minutes is how long it took for me to throw up if I forgot and took my pill on an empty stomach. So, yeah, sounds about right for how long it takes to get into the bloodstream.

The bottom line is that the packet instructions are pretty clear, if they don't seem clear in your particular circumstances you should ask your doctor, and that we know this stuff because it has been subject to scientific tests and FDA approvals.

If you personally are not sure whether the birth control pills you are taking will be effective considering how many days you have been taking them, you should use another form of birth control until such time as you can be sure.
posted by Sara C. at 9:16 PM on November 3, 2016 [2 favorites]

According to this article, "the average amount of hormones from the pill in women’s blood ranges from 1 to 6 nanograms per milliliter of levonorgestrel (the progestin) and 10 to 80 picograms per milliliter of ethinyl estradiol (the estrogen). The amount changes depending on how many hours ago the woman took the pill, peaking after about two hours and then going down. The body clears all the hormones from the pill within 36 hours—that’s why you’ve got to take one every day for it to work."
posted by invisible ink at 10:13 PM on November 3, 2016

Here's a graph comparing concentration of ethinyl estradiol in the blood over time in users of combination pills versus patch users. If you want more scientific search terms, try 'pharmacokinetics' and use "combined oral contraceptive" or similar instead of "birth control pill."
posted by treehorn+bunny at 10:46 PM on November 3, 2016 [7 favorites]

You're interested in the pharmacokinetics and pharmacodynamics of this drug. Try those search terms.
posted by i_am_a_fiesta at 7:04 AM on November 4, 2016

Pharmacokinetics and pharmacodynamics aren't the only important things, though. If suppressing ovulation occurs by preventing some event which occurs several days before ovulation, than you'd need to start taking the pill before those events.
(I'm in a rush right now, but what I'm thinking about are all the signals that the body sends to start an egg maturing which will eventually be released during ovulation. It's possible that the pill is interfering with those signals, instead of the actual release of the mature egg itself. I just don't remember which it is.)
posted by wyzewoman at 9:22 AM on November 4, 2016

Thank you for the recommendations for search terms, that helped a lot. Searching 'oral contraceptives' rather than 'birth control' changed my results substantially!

Although somewhat tangential, this article Missed Hormonal Contraceptives: New Recommendations had some interesting information, particularly p. 1053-1054, on how oral contraceptives suppress ovulation.
posted by twill at 4:00 PM on November 4, 2016

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