OMG! You just realised you forgot to take the pill! Is this reason to panic? Perhaps not. Read on.
How long was it ago that you took the last one? If this was less than 36 hours ago, there's no problem. Just take the pill that you forgot as soon as possible and the next one at the normal time. So: if you take the forgotten pill within 12 hours from the time that you would normally have taken it, you're in the clear.
Was it more than 36 hours ago that you took your last pill? This might be a problem. It depends on the week that you forgot it in.
Most birth control pills need to be taken daily for three weeks, followed by a week in which you take no pills. Some pills you take every single day, no stop week, but usually the fourth week then consists of placebo pills. This advice is only valid for combined pills (pills with progesterone and estrogen) that are taken during three weeks, followed by a stop week. Some pills like the mini-pill should be taken on a much tighter time schedule and the following information is not valid for those. Check with your doctor. We will number the pills in your strip 1 through 21. Pill one is the first one you take after the stop week.
If you forgot a pill in the first week, i.e. pill 1 through 7, this means that ovulation might have taken place. You should take the pill you forgot, finish the strip as you would normally, and use extra contraception for the next seven days as the pill won't be safe during that time. If you had sexual intercourse between 7 days before and 7 days after forgetting your pill, there is a possibility you've gotten pregnant. Consult your doctor about what to do next. Until 72 hours after unprotected sex, a morning after pill is an option.
If you forgot a pill in the second week, i.e. one of pills 8 through 14, you should take the forgotten pill and continue taking your pills as you would normally. Safety of contraception is still guaranteed.
If you forgot a pill in the third week, i.e. one of pills 15 through 21, you can choose one of the following options to continue the protection against pregnancy the pill gives you:
- Take the forgotten pill, take a pill daily for at least seven more days, then insert a stop week. After this week start the normal procedure again with a full strip. To avoid confusion with partly used pill strips, you can finish the strip you started in the minimum seven days and then follow with a stop week - this could mean that you take two strips one directly after the other without stopping in between.
- Do not take the forgotten pill, but start the stop week immediately. The stop week should last no more than seven days, including the day you forgot to take the pill. After the stop week, resume your normal schedule.
- If you take none of the methods mentioned above, you should use condoms until your next menstruation.
To summarize: If you forget to take your pill in the first week, you might be in trouble. Use extra contraception like condoms for the next week (I tend to use them for the rest of that month to be safe) and make sure you're not pregnant.
If you forget in the second week, you should be okay.
If you forget in the third week, you're okay as long as you take care finishing your pill strip in the right way: either start your stop week immediately, or continue taking pills for at least seven days and then take a stop week.
If you're on a pill scheme that is not easily recognizable as three weeks on, one week off, then you should not follow the above advice but consult your doctor instead. If you think you might be pregnant, also consult your doctor. The above advice comes from my own pharmacy as well as a Dutch website run by pharmacists, but if you don't trust it, CONSULT YOUR DOCTOR. Thank you :)
Thanks to Posmella for useful additions to this w/u! | 
