Emergency contraception

Emergency contraception is a method of preventing pregnancy after unprotected sex or if your other contraception has failed. It is not 100% effective. Pregnancy can still occur.

Methods of Emergency Contraception

There are three methods of emergency contraception:

Progestogen only pills — Levonorgestrel
Progesterone receptor modulator — Ulipristal acetate (ellaOne)
Copper IUD (intra–uterine device) inserted into the womb.

All three methods can be very effective but within a certain time limit.

How does emergency contraception work?

Progestogen-only pills — Levonorgestrel:

Inhibits ovulation for 5–7 days, by which time any sperm in the reproductive tract will have become non-viable.

Progesterone receptor modulator — Ulipristal acetate:

Delays ovulation.
Inhibiting implantation

The IUD:

Copper is toxic to the egg and sperm.
Therefore the copper-bearing intrauterine device (CuIUD) is effective immediately after insertion and works mainly by inhibiting fertilization.
If fertilisation has already occurred, there is an anti-implantation effect.

Is emergency contraception for me?

You may be feeling that your situation is quite urgent, but it is also important to consider how progestogen-only pills work. Depending on the time in your menstrual cycle that you take the pills, it works in different ways.

Taken before you ovulate (release an egg) it prevents the egg being released. It is not thought to be effective after fertilization has taken place.

Progesterone receptor modulator

If administered suppresses ovulation if taken immediately before ovulation.
If taken after ovulation it makes it harder for the fertilized egg to implant in the womb.

If you are taking any other medication, you will need to consult a doctor before taking emergency contraception pills.

The IUD does not prevent an egg being released. It can prevent an egg from being fertilised, but it can also prevent a fertilised egg from implanting. It is important that you consider carefully what this means for you.

To understand this better, you may find it helpful to look at the Pregnancy Timeline on the BBC News website.

What is the time limit for emergency contraception?

Emergency contraception progestogen-only pills need to be taken within 72 hours after unprotected sex. They are 95% effective if taken within 24 hours; 85% effective if taken within 25–48 hours and 58% effective if taken within 49–72 hours.
Progesterone receptor modulator — Ulipristal (ellaOne) is for use up to 120 hours after unprotected sexual intercourse (UPSI) or contraceptive failure. It is thought to perform slightly better than the progestogen-only pill.
An IUD can be inserted up to 5 days after you had unprotected sex or up to 5 days after the time you could have ovulated (released an egg). An IUD is effective in 98% of cases.

What are the side-effects of emergency contraception?