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woman getting injectable contraception

This contraceptive method involves an injection of the hormone progestin, which prevents pregnancy for about three months (12 weeks). Contraceptive injections are about 99% effective when used correctly. The injection needs to be renewed on time every 12 weeks.

Progestin is the artificially produced form of the natural hormone progesterone. When given as an injection, it suppresses ovulation by tricking your body into thinking that you are already pregnant.

Contraceptive injections do not protect against sexually transmitted infections (STIs).

How Do Progesterone Injections Work?

Progesterone injections are usually given in the bottom (sometimes the leg or the arm), during the first five days of the menstrual cycle. This way, you are immediately protected. Only healthcare professionals can give you a contraceptive injection, so you need to visit your GP if you are interested in using this method of contarception.

Progesterone - or progestin to be precise - works by stopping your ovaries from releasing an egg each month (ovulation), and by thickening the tissues in your cervix (neck of the womb) so that sperm can not get to the Fallopian tubes, which lead to the ovaries.

Once injected into a muscle, progesterone is gradually released into the body, providing three months protection against pregnancy.

The hormone also thins the lining of your uterus, making it more difficult for a fertilised egg to implant.

The follow up injection can be given up to 14 days before the end of the three months (between weeks 10 and 12).

How Effective Are Progesterone Injections?

In ideal use (meaning the injection is renewed on time), the protection is above 99% effective over a period of two years. UK statistics show that due to the way the injections are actually used (women forgetting to have them renewed on time) the effectiveness is 97%, which nonetheless makes it one of the most effective forms of contraception along with the pill, condoms and intrauterine devices.

Advantages Of Contraceptive Injections

The contraceptive injection is suitable for women who cannot take the combined oral pill. The injection itself is safe and allows you to forget about contraception when having sex – at least for three months.

It provides the same benefits as other hormonal contraceptives such as less painful and lighter periods (sometimes none at all) as well as a reduced risk of cancer of the uterus.

By thickening the cervical mucus, progesterone injections also provide protection from pelvic inflammatory disease (PID), which causes ectopic pregnancy and miscarriages, by preventing bacteria to travel into the uterus.

Other advantages of the progesterone injections include :

  • Women who are breastfeeding can use it
  • Very few interactions with other drugs, including antibiotics
  • Women over 35 can use it (even if it may or may not affect the effectiveness)
  • It can help with diseases such as sickle cell anaemia, endometriosis and uterine fibroids

Progesterone Injection Side Effects

Even though the progesterone injection only provides reliable protection for three months, its effects may last up to a year in some women (generally two to three extra months).

Progesterone injection side effects are not common, but they are similar to the side effects caused by other hormonal contraception methods, such as headaches, breast soreness, weight gain, abdominal pain, mood swings.

While a progesterone injection tends to reduce bleeding and pain in periods, some women may encounter the opposite symptoms. Some women stop using contraceptive injections because of this. In some cases, irregular bleeding may continue for a few months after the last shot.

Further Risks

Using the injectable contraceptive for more than two years can cause thinning of the bones. This is mostly a problem for women at risk of or suffering from osteoporosis. Bone density returns to normal once women stop using the injections.

Because they affect bone density, progesterone injections are not recommended for women under 18, since their bodies are still growing. Young women in their early 20s are also advised to try other methods of contraception first.

Precautions On Use

The progesterone injection is not suitable for you if:

  • You are pregnant
  • You have just given birth (it's usually preferable to wait 6 weeks)
  • You had or have breast cancer
  • You suffer from vaginal bleeding between periods
  • You have had a heart attack or stroke in the past few months
  • You suffer from high blood pressure, blood clots, diabetes or a liver disease

When in doubt, consult your doctor or local health provider to discuss your options.

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