Birth control pills have been around for a long time, but if you have never used them before and are contemplating taking them to prevent pregnancy, it helps to know how exactly they work as well as their pros and cons.

It’s also important to know that the Pill is not recommended for everyone, so you should speak to your family physician or gynaecologist to find out if this birth control method is suitable for you.

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According to Dr Seng Shay Way, a specialist in obstetrics and gynaecology and a consultant at Raffles Women’s Centre, Raffles Hospital, the type of birth control method a woman chooses is dependent on many factors, including age, frequency of sexual activity, family history of certain illnesses, comfort level when it comes to using a particular method of birth control, and evel of desire to fall pregnant in the future. If you are older and have already completed your family, other forms of contraception, such as the intrauterine contraceptive device or hormonal implants may be more suitable.

“You may use a combination of contraceptive methods at a time for extra protection,” Dr Seng points out. “In addition, you can ask your partner to use a condom because it is the only contraceptive method that protects you against most sexually transmitted infections (STIs).”

Here, Dr Seng explains what birth control pills are available in Singapore, how they work, their effectiveness rate, and their pluses and minuses.

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Combined oral contraceptive pill

Mode of action: Prevents the release of eggs from the ovaries

Effectiveness: 99 per cent

Pros: The effects are reversible; minimises menstrual cramps; makes periods regular; reduces acne; reduces the risk of developing ovarian and endometrial cancer; useful for severe premenstrual syndrome

Cons: Has to be taken daily; smokers above 35 years old cannot use it; no protection against STIs; not suitable for women with conditions such as high blood pressure, diabetes for more than 20 years, damage to the arteries, vision, kidneys or nervous system caused by diabetes, gallbladder disease, history of blood clots, stroke, breast cancer, severe migraine, or women who are on medication for seizures

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Progesterone-only pill

Mode of action: Progestin is a female hormone that works by preventing the release of eggs from the ovaries (ovulation) and by changing the cervical mucous and the lining of the uterus.

Effectiveness: 97 per cent to 99 per cent effective when used correctly

(must be taken at the same time every day)

Pros: Suitable for women who do not want to or cannot take estrogen; useful for women who have migraine headaches, who are breastfeeding, who smoke cigarettes, adolescents, or older women above 40 years old

Cons: Has to be taken at the same time daily. Side effects include spotting or break-through bleeding, which can last for a few days until your body gets used to the medicine or for as long as you are taking it; not having a period is also common. Other side effects such as acne, mood swings, nausea, dizziness, bloating, weight gain, headache, and/or hair thinning are rare. Not for women who have liver disease or blood clots, who are on medication for seizures or who have a history of breast cancer.

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Post-coital/emergency contraception pill

Mode of action: This works by preventing ovulation. The hormone in the morning-after pill also prevents pregnancy by thickening a woman’s cervical mucous. The mucous blocks the sperm and keeps it from joining with an egg. The hormone also thins the lining of the uterus. In theory, this could prevent pregnancy by keeping a fertilised egg from attaching to the uterus.

Effectiveness: 75 per cent to 90 per cent

Pros: This is emergency contraception

Cons: Ideally it must be taken between 48 and 72 hours of having unprotected sex. Side effects include nausea and throwing up (If you vomit within two hours after taking the pill, another consultation may be needed to discuss whether a repeated dose is required), breast tenderness, irregular bleeding, dizziness and headaches. Do not use emergency contraception as a form of ongoing birth control – the morning-after pill doesn’t offer lasting protection from pregnancy. If you have unprotected sex in the days and weeks after taking the morning-after pill, you’re at risk of becoming pregnant.