Comparing contraceptive pill types: Combination, mini-pills and more

When the first birth control pill was introduced in 1960 it was a revolution in contraception. For the first time, women could take control of their own reproductive cycles. According to Dr Eve Espey, the contraceptive pill ushered in "a whole new world for contraception." Espey is an associate professor in obstetrics and gynaecology. She tells us it was the first time there was any kind of hormonal contraceptive "or any alternatives to condoms".

Half a century later and despite the introduction of IUDs, patches, injections and the female condom, the pill remains the No. 1 form of contraception. It's used by an estimated 3.5 million women in the UK and 100 million women worldwide. According to Dr Paula Hillard, "When you say ’birth control' most women think of birth control pills." A professor of obstetrics and gynaecology, Hillard says that contraceptive pills are still widely popular, especially among younger women.

Today's contraceptive pills contain a much lower dose of oestrogen than their predecessors. That means they have fewer side effects. Nevertheless, they're still highly effective.

There are two basic types of contraceptive pills. Combination pills combine oestrogen and progestogen. The "mini-pill" contains progestogen only. There are also two types of emergency contraceptive pill, which are taken after unprotected sex.

Here is an overview of each type of pill and an explanation of how it works.

Contraceptive pill type: Combination pills

Combination contraceptive pills are the type most commonly associated with the term "the pill." They contain a combination of the hormones oestrogen and a synthetic form of the hormone progestogen.

Ovulation normally occurs when a spike in oestrogen levels signals the ovaries to release an egg. Combination pills prevent ovulation by adjusting hormone levels to prevent this spike. They also thicken cervical mucous to prevent sperm reaching the egg. In addition, they change the lining of the uterus to make it more difficult for a fertilised egg to implant.

Most combination pills use the same form of oestrogen - ethinylestradiol - but different types of progestogens. The strength of the oestrogen and progestogen can vary too. Depending on how much oestrogen is in the product, the pill will be referred to as low strength or standard strength. When possible, a low-strength pill will be prescribed to help reduce the risks of possible side effects.

Most combination pills come in 21 or 28 day packs. With a 21-day pack, all of the pills are active. You don't take any pills for the last seven days of the cycle. It's up to you to remember when to start the next pill pack. With a 28-day pack, you take 21 active pills followed by seven inactive placebo pills.

Combination pills are also available in three different phase-types: monophasic, biphasic, and triphasic.

• Monophasic: All of the 21 active pills contain the same level of hormones.
• Biphasic: The 21 active pills contain two different doses of oestrogen and progestogen.
• Triphasic: The 21 active pills contain three different doses of hormones. The dose changes every seven days.