rerun image 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.

So Many Choices

Most birth control pills contain two hormones, estrogen and progestin.

Estrogen

The same kind of estrogen is in all low dose pills. The exact dose of estrogen may have an impact on the kind of side effects you experience.

Some women should not take pills with estrogen. Women who are breastfeeding, have a history of blood clots, or have high blood pressure may be better off with a progestin-only pill, which has a slightly lower efficacy level than the combination pill.

Progestin

Different brands of the pill may contain one of many types of progestins. Different varieties of progestin can have different side effects on different individuals.

Monophasic vs. Triphasic

Within the family of estrogen-containing pills, there are two main types: monophasic and triphasic. As the names suggest, monophasic pills provide the same level of hormones throughout the pill cycle. Triphasic pills also induce a steady state of hormones, but at three different levels during the cycle. The two types are equally effective for pregnancy prevention.

"Work with your doctor to figure out which one might be right for you," suggests Holly Hughes, RN, a staff nurse at the Brigham Ob-Gyn Group in Boston. "Just because someone else had a great experience with a certain kind of pill doesn't mean you will."

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.

Negative Side Effects

The most common complaint is about breakthrough bleeding. If you are new to the pill or have recently switched types, you should give your body three months to adjust.

Some women believe that they will gain weight when taking the pill, but a study reported that the pill has no major effect on weight.

Other possible side effects include headaches, nausea, breast tenderness, and bloating. If the negative side effects last for more than three months, talk to your doctor and consider changing brands.

Positive Side Effects

Many people experience skin improvements. For example, particular types of the pill may improve acne. Also, use of the pill decreases a woman’s risk for subsequent ovarian cancer,endometrial cancer, and perhaps colorectal cancer.

Your Period on the Pill

Your pills may come in packages of 21, 28, or 91.If there are 21 pills, take one pill at the same time each day for 21 days. After seven days of not taking a pill, start a new pack. You will have your pediod during the break. If your pack has 28 pills, take one pill at the same time each day for 28 days. The last seven pills do not contain hormones. When you are taking these pills, you will have your period. Some pills come in packages of 91 pills (also called continuous dosing or extended use). The first 84 pills contain hormones, but the last seven do not. You will have your period during the seven days with no hormones.

Oops, I Skipped a Day…

Taking a week off after three weeks of active hormones is part of a normal pill cycle, but skipping days in the middle of the three weeks is not a good idea.

When you take oral contraceptives, the hormone thins out the lining of the uterus making it unable to host egg implantation, and the mucus in the cervix thickens, making it tough for sperm to swim through. These benefits go away if you miss a day, increasing your risk for pregnancy.

If you do miss a pill, take it that day as soon as you remember. Or double up (take two pills) if you do not remember until the next day. You should use another method of contraception if you forget to take two or more pills. Call your doctor or nurse and ask for advise. Complete directions for what to do are also included under the patient package-insert 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 medicines you take, as well as any over-the-counter or herbal medicines.

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