curiousgirl asks:

I
have been on the pill for over 2 years, and have never missed a pill. I
just started my inactive pills on Sunday of this week, and had sex with
my boyfriend on Monday. He wore a condom but I am still concerned there
is a chance I might still get pregnant. Is it possible for this to
happen or am I safe?

Heather replies:

So
long as you take your pills as directed and on time, with the exception
of a few medications or herbs that can interact with the pill, you’re
as covered as you get.

I get questions like this a lot, so in the interest of making sure
you and everyone else understand your pill as best you can, let me
explain how the pill works and thus, why it works just the same during
the placebo period (the time you take or have the inactive pills) as it
does during the other three weeks of your pill cycle.

If you understand how your menstrual and fertility cycle works when you aren’t on oral contraceptives (and if you don’t, read this before reading further), it’s easier to understand how the pill works.

During a normal, unmodified fertility cycle, everything that happens
is first driven by the signals your brain, via the hypothalamus and
your pituitary gland, sends your reproductive system. Based on those
actions, the release of an egg by the ovary during a normal cycle also
releases hormones which direct the rest of the cycle, including the
type of vaginal secretions you’ll have for the best sperm mobility
during the fertile period.

When you menstruate, it’s because the egg released by the ovary
either wasn’t fertilized, or was fertilized but did not implant in the
uterus, so your endometrium which has built up from all of those
directives, to prepare for a fertilized egg implanting, then sloughs
itself off. That’s what your flow is during menses (which is also why
sometimes it has little globs in it, rather than just fluid).

When you take the pill, the synthetic hormones send a different set
of signals to your reproductive system entirely, so that you do not
ovulate — release that egg — so that your vaginal secretions become
and remain thicker (to make it tougher for sperm to get to an egg in
the case something went amiss there), and so that that endometrial
lining doesn’t build up as much (in the case that the other two modes
go awry, that would make it really tough for a fertilized egg to
implant). That’s three different ways to protect you from pregnancy,
and even just one of those ways is often enough.

The reason why you don’t have any extra risks during that placebo
week is because of all of the things the pill has done in the three
weeks prior, and which it will do once you start taking it again.
During that week, you don’t need pills because they’ve already
prevented ovulation and fertilization, so you couldn’t become pregnant
during that period of time, as without all those preceding signals to
be fertile, you can’t suddenly become fertile in that week.

Sometimes this is all more simply explained by saying that the pill
tricks your body into thinking it is already pregnant each cycle, which
is an accurate way to put it, since similar things do occur when a
woman is pregnant, and since you can’t become pregnant again once you
already are.

For more on how the pill works, one of my favorite explanations in visual format is on the PBS site about the pill, here. The Feminist Women’s Health Center also has a great general page about the pill, including loads of extra links.

While there are certainly downsides and risks with taking the pill,
one thing that isn’t a downside is how incredibly effective it is: in
perfect use, the pill is very close to 100% effective. When you combine
it with condom use — — which is always wise, since the pill offers so
STI protection — which are around 98% effective in perfect use, you have an awesome combined method that is beyond unlikely to fail.

Just be sure that you are taking your pills as directed — and if
you’ve lost your pill insert and need a reminder on what that means, check this out
— and on time, and it’s all good. Keep combining your pills with
condoms and I really can assure you that there is just no sound reason
to be worrying yourself about pregnancy. Obviously, no method, even a
combined one, is 100% effective, but right now, you’ve got as close as
it gets.