The mechanism of how levonorgestrel (LNG) act as an emergency contraception is not well understood. The mode of action is thought to be by inhibiting ovulation rather than inhibiting implantation (1)
- if taken before ovulation, LNG will inhibit ovulation for about 5–7 days by which time the sperm in the upper reproductive tract will loose its fertilising ability (1)
Previously the regimen involved taking two 750 mcg levonorgestrel tablets and repeating the dose 12 hours later; however since October 2003 giving 1.5 mg as a single dose has become the licensed norm in the UK (2)
- Levonelle 1500 (levonorgestrel 1.5 mg) became a prescription only medicine from the 1st of November 2005 (3)
- can be used at any time during the menstrual cycle but should not be administered if menstrual bleeding is overdue (4)
LNG should be taken as soon as possible preferably within 12 hours and no later than 72 hours of unprotected sexual intercourse (4)
- use of levonorgestrel between 73 and 120 hours after unprotected sex could be considered outside the product license but women should be informed about the limited evidence of efficacy (1)
- LNG could be used more than once in a cycle if indicated clinically (but repeated use is not recommended since it may cause disturbances to the menstrual cycle) (1)
- if unprotected sexual intercourse occurs within 12 hours of taking LNG as emergency contraception further emergency contraception therapy is not required (1)
A study compared the use of the Yuzpe regimen (Schering PC4 - each tablet containing 50 mcg of oestradiol plus 250 mcg levonorgestrel - taking two tablets and repeating the dose 12 hours later) with the levenorgestrel method. The study involved nearly 2,000 women being randomized to either the Yupze regimen or to the levenorgestrel method; the cut-off point for enrolment was 72 hours after coitus.
- the overall pregnancy rate was 1.1 % for the levonorgestrel method and 3.2% for the Yupze regimen.
- for both regimens, the earlier the treatment was initiated the more effective it was
- there was a higher rate of nausea and vomiting in women given the Yuzpe regimen
Adverse effects of levonorgestrel include:
- vomiting & nausea
- vomiting is unusual (occurs in 1% of women), nausea is seen more frequently (in around 14%)
- if the patient vomits within 2 hours of administration of LNG, a further dose should be taken as soon as possible
- disturbances in the cycle
- breast tenderness
- ectopic pregnancies (1,6)
- (1) Faculty of Family Planning and Reproductive Health Care Clinical Effectiveness Unit. FFPRHC Guidance (April 2006). Emergency contraception. J Fam Plann Reprod Health Care. 2006;32(2):121-8
- (2) Lancet (1998), 352, 428-33
- (3) Faculty of Sexual and Reproductive Healthcare (FSRH) 2006. Faculty statement from the CEU on Levonelle 1500 and the use of liver enzyme inducing drugs
- (4) ABPI Medicines Compendium 2009. Summary of product characteristics for Levonelle 1500 microgram tablet
- (5) Von Hertzen et al. Low dose mifepristone and two regimens of levonorgestrel for emergency contraception: a WHO multicentre randomised trial. Lancet. 2002 Dec 7;360(9348):1803-10.
- (6) Pulse 2004; 64 (24): 51.
- (7) Sanfilippo J, Downing D. Emergency contraception: when and how to use it. J Fam Pract. 2008;57(2 Suppl Emergency):S25-36