How effective is emergency contraception?-Your contraception guide
It depends which type of emergency contraception you use and how soon you use it.
There are 2 methods of emergency contraception:
- thecopper intrauterine device (IUD), or coil, which is the most effective type of emergency contraception.
- the emergency contraceptive pill, or morning-after pill. There are 2 types of emergency contraceptive pills – Levonelle and ellaOne.
Emergency contraception prevents pregnancy if you have not used contraception or think your usual method of contraception has failed.
紧急避孕不应用作通常的避孕方法。
Both types of emergency contraception are effective at preventing pregnancy if they are used soon after unprotected sex.
All women who need emergency contraception should be offered the copper IUD (if appropriate or acceptable), as it is the most effective form of emergency contraception.
Less than 0.1% of women who choose the IUD become pregnant, whereas pregnancy after taking the emergency contraceptive pill is not as rare. It's thought ellaOne is, on average, more effective than Levonelle.
The IUD (coil)
The IUD is the most effective form of emergency contraception. Trials suggest the failure rate for the IUD as emergency contraception is lower than 0.1%. This means less than 1 woman in 1,000 using the IUD as emergency contraception will become pregnant.
The IUD must be fitted by a healthcare professional within 5 days (120 hours) of having unprotected sex or, if it's possible to estimate when you ovulate, up to 5 days after you ovulate.
紧急避孕药
Levonelle contains levonorgestrel and has to be taken within 72 hours (3 days) of unprotected sex. EllaOne contains ulipristal acetate and is licensed to be taken within 120 hours (5 days) of unprotected sex.
Levonelle和Ella酮都只有在从卵巢中释放出鸡蛋之前才有效(ovulation). The sooner you take Levonelle or ellaOne, the more effective it will be.
Ovulation is triggered by rising levels of a hormone called luteinising hormone (LH).
Levonelle appears not to be effective after levels of LH start to rise. EllaOne continues to be effective a little later in the cycle.
2017年对证据的审查估计，在无保护性行为后大约有1-2％的妇女会怀孕。相比之下，据估计，在未受保护的性行为后服用莱沃内尔的女性中有0.6％至2.6％会怀孕。
The effectiveness of both Levonelle or ellaOne may be reduced if a woman has a highbody mass index (BMI). This makes it harder to provide a more precise estimate for either pill.
Get medical advice if you vomit within 2 hours of taking Levonelle or 3 hours of taking ellaOne. You'll need to take another dose or have an IUD fitted.
Find out more aboutemergency contraception, including how it works and possible side effects.
Page last reviewed: 22 August 2019
Next review due: 22 August 2022