Sheela Nair, a newly wed from Trivandrum, was looking for an effective and easy-to-use form of contraception. 

Various forms of contraception are available in the market, today, and Sheela found the choices overwhelming. So, she visited a doctor who prescribed oral contraceptive pills, one of the most effective methods of preventing conception.

Most women, like Sheela however, take "the pill" without proper knowledge of the basics of contraception. In fact, a nationwide survey conducted in the United States revealed that most women were equipped with very little information about oral contraceptive pills. "After 40 years of use, we take for granted that women are fully informed about the Pill, but I find that many of my patients are not," said A George Thomas, clinical associate professor, Mount Sinai Medical Center, New York City.

In this article, we answer most frequently asked questions about 'The Pill'.

• 5 signs that you are pregnant

How do oral contraceptive pills work? Do they contain hormones?

To become pregnant, ovulation (the process of the ovary releasing an egg) must be followed by fertilisation of the egg by a sperm. The fertilised ovum must then implant onto the wall of the uterus.

Oral contraceptive pills prevent pregnancy primarily by suppressing ovulation.

Progesterone (hormone involved in the female menstrual cycle) in birth control pills thickens your cervical mucus (a secretion of the cervix which moistens and protects this region of the body). The consistency of cervical mucus changes during a woman's menstrual cycle and can hinder the travel of sperm to the uter, making it hard for sperm to enter the cervix and fertilise the egg, if it is released.

It might also make the coating of the egg thicker and tougher to penetrate. Progesterone also thins the lining of the uterus. This means that even if an egg were to be fertilised, implantation onto the uterine wall would be unlikely.

Is this method foolproof?

If used correctly and consistently, the pill is projected to be about 99.7 to 99.9 percent effective in preventing pregnancy. The failure rate of hormonal methods of contraception, including the pill is usually lower than non-hormonal methods such as condoms and Intrauterine devices.

However, if the pill is not taken as prescribed, the chances that you will get pregnant are higher. More mistakes mean greater risk of failure. Though the pill is one of the most reliable methods of contraception, it is effective only when instructions are followed to the letter.

Certain drugs such as sedatives, antibiotics, antiseizure medications and some herbal medicines can reduce the effectiveness of the pill. If you are taking any of these medications, discuss this with your doctor so that you can switch to another form of birth control.

• How to do a home pregnancy test

What kinds of OC pills are available in India?

There are two kinds of pills, combination pills and mini pills.  The mini pill is so called because it contains only progesterone (Cerazette).  However, 99 per cent of all contraceptive pills are combination pills (Marvelon, Ovral-L, Triquilar, Femilon, Triphasil, Diane-35), which contain both estrogen and progesterone in various forms.

Most women who take oral contraceptives are prescribed combination pills because they are slightly more effective than mini pills.

But mini pills are useful in certain conditions, such as breastfeeding, where estrogen cannot be taken.

Your doctor will prescribe the right type of pill for you.

How are these pills taken?

All combination birth control pills come in packages of 21 or 28 pills. Most doctors recommend you start taking them from the sixth day of your menstrual period.

If the pack has 21 pills, then take the pill each day, at roughly the same time, for 21 days.  Then stop taking the pill for sevn days (during which time you will most likely menstruate) and then start again on the next pack of 21 pills.

If the pack contains 28 pills, take a pill a day, at roughly the same time, for 28 days, and then without missing a day, start with the next pack (regardless of your periods).  The reason is that the pack of 28 pills contains not only 21 hormone pills, but also 7 'blank' pills with no active contraceptive ingredients.

What if I forget to take a pill?

Good question. If you forget to take a pill, take it as soon as you remember and take the next pill at the usual time.

If you miss two days, take two pills each day for the next two days and then go back to your usual schedule.

However, if you miss three or more pills, discard the pill strip and use another form of birth control until your next menstrual cycle starts. If your period is delayed or you miss a period, you could be pregnant. Visit a doctor or take the home pregnancy test.

Are there any side effects?

Oral contraceptive pills do have a few side effects. These could be:

~ Mild side effects

Nausea, weight gain (about two kgs), water retention in your tissues, breast tenderness, and at times spotting between periods.  These side effects are common but usually subside in the first three months.

~ Moderately serious side effects

Some women experience breast pain, mild rashes and jaundice; reduced tolerance to contact lenses; headaches or migraines; nervousness and sometimes depression. These side effects are not very common. If you experience any of these, you must contact your doctor.  

~ Serious side effects

One of the major side effects of the pill is formation of blood clots especially in your legs. These clots could sometimes dislodge and travel to other parts of the body. Warning signs are leg tenderness or swelling; sudden chest pain or shortness of breath, partial or complete loss of vision or blackouts; numbness in any part of the body.  If any of these symptoms occur, stop taking the pill immediately and consult your doctor. You might have to switch to another form of contraception.

Who should not take the pill?

It is not recommended for women:

~ Over 35 who smoke. 

~ With high blood pressure, high cholesterol levels, or a family history of heart disease. 

~ With past or present breast, uterus or liver cancer. 

~ Suspecting a pregnancy. There could be other conditions where the pill is contraindicated. A thorough examination and your detailed family medical history will help the doctor see if the pill if right for you. Visit your gynaecologist before you start taking the pill.

How do I choose the right contraception method for me?

Your choice of contraception would depend on various factors including, how important it is for you to not get pregnant, your general health condition, whether you need protection from Sexually Transmitter Diseases, the cost, how comfortable you are with it and so on.

Click here to get a quick overview of the different methods of contraception and compare them.
Next week: 10 myths about oral contraceptive pills, busted 

-- The author has an MBBS from KEM Hospital, Mumbai, with a Masters in Nutrition from the University of Texas at Austin.