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Intrauterine Devices (IUDs): What is the difference between them and how do they work?

Many women consider intrauterine device (IUD) as a form of birth control both before having a baby, and after.  This is because the IUD is very reliable, safe, and is as effective as permanent sterilization.  These features make the IUD a very desirable birth control option.

There are two main types of IUDs available on the market today: the copper IUD and the hormonal IUD. 

Both types of IUDs are small plastic T-shaped devices that inserted into the uterus by a trained medical professional.  The copper IUD and the hormonal IUD act similarly in that they are both foreign bodies inside the uterus that induce local inflammation and prevent implantation of an egg into the uterine lining. 

Benefits of IUDs:

  • 99% effective at preventing pregnancy
  • Long acting (3-10 years depending on device)
  • Reversible once device removed
    • Similar pregnancy rates as compared to non-IUD users
  • No need to rely on user adherence
  • Few side effects
  • Few reasons why women are not candidates for use
    • Anatomic abnormalities, active pelvic infection, current pregnancy, unexplained abnormal uterine bleeding, current breast cancer
  • Avoid excess hormones from oral birth control pills

Copper IUD

  • How does it work?
    • Copper increases the inflammatory response inside the uterus and prevents implantation of an egg
    • Copper kills sperm
    • Does not impact ovulation
  • How long can it stay in?
    • 3-10 years depending on the device used
  • Advantage of copper IUD over hormonal IUD
    • Can be used for emergency contraception if inserted within 5 days of unprotected sex
    • Continued menstrual cycle while IUD in place
    • No hormone side effects whatsoever
    • Keep it in for longer
  • Disadvantage of copper IUD over hormonal IUD
    • Potential higher risk of pelvic inflammatory disease if exposed to a sexually transmitted infection (use a condom!)
    • Period may be heavier, longer or more painful

Hormonal IUD (Progestin IUD)

  • How does it work?
    • Contains levonorgestrel, a progestin hormone, that thickens cervical mucus and impairs implantation of an egg
    • Stops the lining of the uterus from growing as thick so an egg is less likely to implant
    • Local hormone effects, very little hormone is absorbed into the bloodstream (about 10 times LESS than taking a progestin only pill)
    • Ovulation rates vary depending on device used
  • How long can it stay in?
    • 3-5 years depending on device used
  • Advantage of hormonal IUD over copper IUD
    • Slightly more effective at preventing pregnancy
    • Progestin can make your period lighter or nearly absent and can reduce cramping during your cycle
    • Can be used for heavy menstrual bleeding or endometriosis
  • Disadvantage of hormonal IUD over copper IUD
    • Some women may still have hormone side effects of the very small amount of progestin hormone
    • Cannot be used as emergency contraception
    • Must be removed and reinserted more frequently

This post was co-authored by Erin Manchuk, BScPharm, BCGP and Stephanie Liu, MD, MSc, CCFP, BHSc.


Phillips SJ, Tepper NK, Kapp N, et al. Progestogen-only contraceptive use among breastfeeding women: a systematic review. Contraception 2016;94:226–52.

Cleland K, Zhu H, Goldstuck N, et al. The efficacy of intrauterine devices for emergency contraception: a systematic review of 35 years of experience. Hum Reprod 2012;27:1994–2000 (Accessed 28 June 2019) (Accessed 1 July 2019)

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