Levonorgestrel

How it works

Levonorgestrel mimics progesterone, principally inhibiting or delaying ovulation and thickening cervical mucus; in intrauterine use it also produces local endometrial suppression.

Prescribing in practice

• As emergency contraception it is more effective the sooner it is taken after unprotected intercourse and works mainly by delaying ovulation, so it is ineffective once ovulation has occurred and does not disrupt an established pregnancy.
• Efficacy of oral emergency contraception may be reduced by enzyme-inducing drugs and in women of higher body weight, where an alternative such as a copper intrauterine device should be considered.
• Vomiting shortly after an oral dose may require a repeat dose, and irregular bleeding can follow use.

Monitoring

No routine laboratory monitoring is needed; advise a pregnancy test if the next period is delayed and review contraceptive plans.

Counselling the patient

• Take emergency contraception as soon as possible after unprotected sex for best effect.
• Seek advice and take a pregnancy test if your period is more than a few days late.
• This does not protect against future episodes or against sexually transmitted infections.

Evidence & guidelines

WHO and NICE-aligned guidance support levonorgestrel for emergency contraception, noting reduced efficacy compared with a copper intrauterine device and after ovulation has occurred.