How the Noristerat Contraceptive Injection Works

The Noristerat injection is a reversible, progestin-only method of prescription birth control. It is not available in the United States, but it is common in the United Kingdom, Europe, Africa, and Central and Latin America. Noristerat is a contraceptive injection that contains the progestin hormone, norethisterone enantate.

The effectiveness, advantages, and disadvantages of Noristerat are similar to Depo Provera but its duration of action is shorter (Noristerat lasts for eight weeks as compared to Depo Provera, which lasts for 12 weeks). Noristerat does not offer any protection against sexually transmitted infections.

Noristerat is also known as Doryxas, Norethisterone injectable, Norigest, Nur-Isterate, Syngestal, and Unidepo.

Doctor holding syringe
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Noristerat is a contraceptive that is injected into the muscle of the buttock. The injection is usually given during the first one to five days of your monthly period. Noristerat will continuously release progestin into your bloodstream over a period of eight weeks (two months).

After eight weeks, you can only have one more Noristerat injection.


Noristerat is meant to be a short-term method of contraception. It is mainly used by women under these circumstances:

  • Their partner is having a vasectomy (the Noristerat injection will offer pregnancy protection until the vasectomy becomes effective).
  • They are being immunized against rubella.

Noristerat does not have any estrogen, so this injection may be a good short-term birth control method if you cannot use estrogen-based contraceptives. It is also a contraceptive option if you are breastfeeding.

How It Works

The norethisterone protects against pregnancy mainly by preventing ovulation. Towards the end of the eight weeks, the Noristerat works mainly by thickening your cervical mucus. The hormone may also thin the lining of the uterus.

After the Injection

For the eight weeks that you are using Noristerat, it is important for you to check your breasts and nipples once a month for any changes (such as dimpling of the skin or lumps). If you need to have blood work done, make sure that your healthcare provider knows that you are using Noristerat. This is because Noristerat may affect some of your results.

Your healthcare provider also needs to be aware that you have had the Noristerat injection if you are going to undergo any surgery during the eight-week time frame. Keep in mind that once you stop taking Noristerat, it can take up to a month longer (than other hormonal methods) for you to start ovulating again and regain your fertility.

Side Effects

Not every person will have side effects from this injection. The most commonly reported Noristerat side effects are:

  • Spotting or breakthrough bleeding
  • Delayed period
  • Irregular or heavier bleeding
  • Weight gain
  • Headaches
  • Dizziness and/or nausea
  • Skin reactions (such as pain, rash and/or itch at the injection site


Noristerat is 97% to 99.7% effective. This means that with typical use, 2 out of every 100 people who use Noristerat become pregnant in one year. With perfect use, less than 1 out of every 100 people who use Noristerat will become pregnant in one year.

If you receive the Noristerat injection during the first five days of your period, then it is effective immediately and no back-up birth control is needed. There are certain medications that can lower the effectiveness of Noristerat.

Frequently Asked Questions

  • What is Noristerat?

    Noristerat (norethisterone enanthate) is a long-acting progesterone-only form of birth control delivered by injection. It is similar in action to Depo-Provera. And, while approved for use in over 60 countries, including the United Kingdom, Noristerat is not licensed for use in the United States.

  • Why is Noristerat not available in the U.S.?

    The Food and Drug Administration (FDA) has long resisted approving Noristerat due to animal studies that suggested it may increase the risk of breast cancer, albeit slightly. It's important to remember that the FDA had the same concerns about Depo-Provera and denied the approval of that drug several times before its eventual licensing in 2004.

  • Who is Noristerat intended for?

    Noristerat is intended for short-term use and may be an option for women who:

    • Cannot use estrogen-based contraceptives
    • Want to continue breastfeeding
    • Are waiting for a partner's vasectomy to become effective
    • Just received the rubella vaccine (to avoid pregnancy and the risk of rubella-associated birth defects)
  • How does Noristerat differ from Depo-Provera?

    Noristerat and Depo-Provera are both long-acting, progesterone-only, injectable contraceptives. Of the two, Depo-Provera is the longer acting, providing 12 weeks of protection from pregnancy compared to eight weeks for Noristerat.

  • Now does Noristerat work?

    Noristerat prevents pregnancy in two key ways:

    • By causing the cervical mucus to thicken, preventing sperm from reaching the ovum (egg)
    • By thinning the lining of the uterus, preventing implantation of the ovum even if fertilization does occur
  • How effective is Noristerat?

    With typical use, Noristerat is around 98% effective. This means that two of every 100 women who use Noristerat will become pregnant within a year. This makes Noristerat one of the more reliable forms of birth control.

  • What are the side effects of Noristerat?

    Not everyone who uses Noristerat gets side effects, but, of those who do, some of the more common include:

    • Spotting or breakthrough bleeding
    • Delayed period
    • Heavier periods
    • Irregular bleeding
    • Breast pain
    • Weight gain
    • Headaches
    • Depression
    • Dizziness
    • Nausea
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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Dawn Stacey, PhD, LMHC
Dawn Stacey, PhD, LMHC, is a published author, college professor, and mental health consultant with over 15 years of counseling experience.