Emergency Contraception: Which Is Most Effective?

After unprotected sex, the most effective method of emergency contraception (EC) is the copper intrauterine device (IUD), according to findings from an intervention review and meta-analysis.¹ However, the copper IUD also is arguably the least convenient method.

To determine which method of EC after unprotected sex is the most effective, safe, and convenient, researchers analyzed 100 randomized controlled trials, 86 of which were conducted in China, that involved a total of 55,666 women.

All EC methods are safe when used as directed. For the oral medications, researchers found that both mid-dose (25-50 mg) and low-dose (< 25 mg) mifepristone were significantly more effective than levonorgestrel. However, the significance was marginalized when only high-quality studies were used. In general, the moderate and low doses of mifepristone had similar effectiveness, but women who took the moderate dose were more likely to have menstrual delay, which is the most common adverse effect of mifepristone, according to the authors.

When taken within 72 hours after intercourse, ulipristal acetate was marginally more effective than levonorgestrel. The effectiveness of mifepristone and ulipristal acetate did not seem to be affected by the time to administration after intercourse, whereas levonorgestrel was significantly more effective at preventing pregnancy when taken within 72 hours after intercourse than when taken 3 days or more after unprotected sex.

A single 1.5-mg dose of levonorgestrel was just as effective as the standard regimen of the drug, which is two 0.75-mg doses of levonorgestrel given 12 hours apart, and the time between intercourse and treatment did not affect effectiveness when directly compared with the timing of the standard regimen. The Yuzpe method-a combination of oral contraceptives that contain levonorgestrel and ethinyl estradiol taken within 72 hours after unprotected sex-was the least effective method of EC.

Estrogen-containing regimens were more likely to cause nausea and vomiting, and progestogen-containing and antiprogestogen-containing methods were more like to alter the menstrual cycle. Menstruation occurred sooner than expected among those who used levonorgestrel and later than expected among those who used ulipristal acetate. 

The copper IUD is the most effective method of EC and the only method with the added benefit of providing ongoing contraception once placed. However, it’s the least convenient method of EC, requiring placement by a gynecologist, nurse practitioner, or certified midwife. Not all providers have received training for insertion of IUDs, and those who have may not have any open appointments during the 72-hour postcoital window.² It is also relatively expensive up front, costing uninsured women $500 to $1000 and up,³ but considering that the copper IUD can be used for up to 10 years, this method is highly cost-effective.

Pertinent Points:
- The most effective but least convenient method of emergency contraception to prevent pregnancy after unprotected sex is the copper intrauterine device.
- The most effective orally administered emergency contraception is mifepristone, but all types of emergency contraception are safe when taken as directed and considered effective, especially when taken within 72 hours after unprotected sex.

References:

1. Cheng L, Che Y, Gulmezoglu AM. Interventions for emergency contraception. Cochrane Database System Rev. 2012;8:CD001324.2. Harper CC, Blum M, de Bocanegra HT, et al. Challenges in translating evidence to practice: the provision of intrauterine contraception. Obstet Gynecol. 2008;111:1359-1369.3. IUD. Available at: http://www.plannedparenthood.org/health-topics/birth-control/iud-4245.htm. Accessed September 28, 2012.