How effective is Twirla compared to other birth control methods?
Medically reviewed by N. France, BPharm. Last updated on Dec 23, 2020.
Twirla is a weekly birth control patch or transdermal system used to prevent pregnancy. It contains ethinyl estradiol and levonorgestrel. Twirla is used in a four week cycle. Each Twirla patch is worn for seven days, with three patches being worn over three weeks followed by a patch free week.
Birth control patches, such as Twirla, are a highly effective form of birth control. Birth control patches are as effective as birth control pills (oral contraceptives) and vaginal contraceptive rings.
When used following the instructions they are more than 99% effective, with only 0.3 out of 100 women using the patch for a year expected to get pregnant. Under typical-use conditions in a real-world setting, 7-9 women out of every 100 women using these forms of birth control would be expected to get pregnant in a year.
Patches are less effective than surgical sterilization, intrauterine devices (IUDs), implants and injections, but more effective than condoms, and diaphragms and sponges used with spermicides.
Why is Twirla less effective in a ‘real-world’ setting?
Twirla, like many other forms of birth control, is less effective in a ‘real-world’ setting (typical use) because women do not always follow the instructions-for-use exactly as directed every time they use birth control. Sometimes a woman might forget to apply or replace a patch at the correct time and sometimes a patch may come loose, for example.
There is less variation in the effectiveness of long-term forms of contraception, such as IUDs and implants, because there’s no need to remember to use or replace it on a weekly basis, like you do with a patch, and they don’t come loose like a patch can.
Not only can how closely the instructions are followed affect how well Twirla works, but how much a woman weighs can also impact on how effective the patches are.
Twirla is less effective in women with a higher body mass index (BMI)
Twirla has been shown to have reduced effectiveness in women with a BMI ≥ 25 kg/m2, which means it is less effective in women who are overweight.
- Food and Drug Administration (FDA). Birth Control Chart. Available from: https://www.fda.gov/consumers/free-publications-women/birth-control-chart. [Accessed December 24, 2020].
- Guttmacher Institute. Contraceptive Effectiveness in the United States. April 2020. Available from: https://www.guttmacher.org/fact-sheet/contraceptive-effectiveness-united-states. [Accessed December 24, 2020].
- Food and Drug Administration (FDA). Twirla. Available from: https://www.accessdata.fda.gov/drugsatfda_docs/label/2020/204017s000lbl.pdf. [Accessed December 24, 2020].
- National Heart, Lung, and Blood Institute, NIH. Calculate Your Body Mass Index. Available from: https://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htm. [Accessed December 24, 2020].
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