The contraceptive injection

Many women complain about the side effects of contraceptive methods, especially the pill. Side effects such as nausea and breast tenderness are deterrents.

An alternative to the pill is the contraceptive injection. It is a long-acting, reversible method. Just fit it and forget it for 12 weeks.

It is regarded as non-user-dependent, that is, its effectiveness as a contraceptive does not rely on the user doing anything, except of course, to remember every 12 weeks to have another contraceptive injection of the hormone, medroxy-progesterone, available here as depo-provera. It's injected in the buttock or arm by a medical doctor or nurse.

Medroxy-progesterone is more than 99 per cent effective. So statistically, fewer than one in 100 women who use this injection properly will become pregnant in one year. This is a better efficacy profile than most other forms of contraception. The woman should not be more than a few days late for her subsequent injection.

If more than a week passes after the woman's due date for re-injection the doctor will ask for a pregnancy test to ensure the woman is not pregnant when she receives her next dose. It is safe for the breastfeeding woman to use six weeks after childbirth, and women who do not intend to breastfeed may receive the injection within a few days after childbirth.

How does it work?

This product has more than one mechanism of action. First, it prevents the release of certain hormones from the brain which control some aspects of the menstrual cycle. Blocking the hormones prevents the release of an egg from the ovaries. No egg, no fertilisation, no conception. It also thickens the mucous made at the neck of the womb (cervix) to form a mucous plug which prevents sperm from entering the womb. It thins the usually thickened lining of the womb. So, in the unlikely event that an egg is fertilised, it will not be able to attach itself to the womb.

The downside of the injection

The injection's effectiveness, however, comes at a price — once the drug has been placed in the system, it cannot be removed. This product takes 12 weeks to wear out of the body, so any side effects will last for all that time.

Side effects with the medroxy-progesterone injection include unpredictable menstrual bleeding. Periods may become heavier, last longer or may stop altogether. Periods may take up to 18 months to restart after the woman has stopped using the injection. Dizziness, headache and weight gain are other side effects. It makes some women prone to osteoporosis or brittle-bone disease.

Dahlia McDaniel is a pharmacist and final year doctoral candidate in public health at the University of London; email: yourhealth@gleanerjm.com.