How the Noristerat Contraceptive Injection Works

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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 doctor knows that you are using Noristerat. This is because Noristerat may affect some of your results.

Your doctor 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, 3 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.

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  • British National Formulary; 66th Edition (September 2013) British Medical Association and Royal Pharmaceutical Society of Great Britain, London.