Although women are grateful for this relatively simple and reliable form of contraception, most of them readily admit that they don't know much about how oral contraceptives actually work.

When you take oral contraceptives, the hormone thins out the lining of the uterus making it unable to host egg implantation. The mucus in the cervix thickens, making it tough for sperm to swim through.

So Many Choices

Most birth control pills contain 2 hormones, estrogen and progestin. Pills that contain both estrogen and progesterone are called combined contraceptives. There is also another type of pill that contains progestin-only, called the mini-pill.

Fewer Side Effects Today

There are fewer side effects now than there used to be because oral contraceptives today contain a much lower level of estrogen. Lower hormone levels usually mean fewer side effects, but side effects do still occur.

Your Period on the Pill

Depending on which kind of birth control pill your doctor prescribes, you could have a pack of 21 pills, 28, or even 90.

If there are 21 pills in the pack, take 1 pill at the same time each day for 21 days. After 7 days of not taking a pill, start a new pack. You will have your period during the break.

If your pack has 28 pills, take 1 pill at the same time each day for 28 days. Since the last 7 pills do not contain hormones, this will be when you will have your period.

Another option is to have 28 pills, but with the final 4 pills being inactive (without hormones). With this kind of pill, your period may be shorter and lighter.

Some pills come in packages of 90 pills (also called continuous-dosing or extended-use). The first 83 pills contain hormones, but the last 7 do not. You will have your period during the 7 days with no hormones every 3 months.

There are also packs with 365 pills. Women take 1 pill a day for a year. Over time, bleeding may become lighter and may even stop.

Oops, I Skipped a Day…

Taking a week off after 3 weeks of active hormones is part of a normal pill cycle, but skipping days in the middle of the 3 weeks is not a good idea. It could increase your risk for pregnancy.

If you do miss a pill, take it that day as soon as you remember. Or double up (take 2 pills) if you do not remember until the next day. You should use another method of contraception if you forget to take 2 or more pills. Call your doctor or nurse and ask for advice. Complete directions for what to do are also included in the instructions that come with your birth control pills.

Talk to Your Doctor

You cannot get birth control pills without a prescription, so you have to see a doctor at some point. Be open with your doctor so that you can make the best decision possible about birth control. Women with certain conditions should not take oral contraceptive. Talk to your doctor about any medications you take, as well as any over-the-counter or herbal medications or supplements.

If you experience problems and side effects, speak up. There may be something out there that's better for you.