The progestogen-only injection is also known as depot medroxyprogesterone acetate (DMPA). You will see it listed as “DMPA” in the UK MEC guidelines. It is given at 12 to 13 week intervals as an intramuscular or subcutaneous injection of medroxyprogesterone acetate (a type of progestin).
The DMPA is more than 99% effective with perfect use, but less effective with typical use (94%). It is less effective with typical use because women may forget to book in for an injection every 12 to 13 weeks.
It can take 12 months for fertility to return after stopping the injections, making it less suitable for women who may wish to get pregnant in the near term.
There are two versions commonly used in the UK, all containing medroxyprogesterone acetate:
- Depo-Provera: given by intramuscular injection
- Sayana Press: a subcutaneous injection device that can be self-injected by the patient
Noristerat is an alternative to the DMPA that contains norethisterone and works for eight weeks. This is usually used as a short term interim contraception (e.g. after the partner has a vasectomy) rather than a long term solution.
Contraindications
UK MEC 4
- Active breast cancer
UK MEC 3
- Ischaemic heart disease and stroke
- Unexplained vaginal bleeding
- Severe liver cirrhosis
- Liver cancer
The DMPA can cause osteoporosis. This is something to consider in older women and patients on steroids for asthma or inflammatory conditions. It is UK MEC 2 in women over 45 years, and women should generally switch to an alternative by age 50 years.
Mechanism
The main action of the depot injection is to inhibit ovulation. It does this by inhibiting FSH secretion by the pituitary gland, preventing the development of follicles in the ovaries.
Additionally, the depot injection works by:
- Thickening cervical mucus
- Altering the endometrium and making it less accepting of implantation
Timing the Injection
Starting on day 1 to 5 of the menstrual cycle offers immediate protection, and no extra contraception is required.
Starting after day 5 of the menstrual cycle requires seven days of extra contraception (e.g. condoms) before the injection becomes reliably effective.
Women need to have injections every 12 – 13 weeks. Delaying past 13 weeks creates a risk of pregnancy. The FSRH guidelines say it can be given as early as 10 weeks and as late as 14 weeks after the last injection where necessary, but this is unlicensed.
Side Effects and Risks
Changes to the bleeding schedule is one of the primary considerations with progestogen-only contraception. Bleeding often becomes more irregular, and in some women, it may be heavier and last longer. This is usually temporary, and after a year of regular use, most women will stop bleeding altogether (amenorrhoea). It is not possible to predict how individuals will respond.
Other side effects include:
- Weight gain
- Acne
- Reduced libido
- Mood changes
- Headaches
- Flushes
- Hair loss (alopecia)
- Skin reactions at injection sites
Reduced bone mineral density (osteoporosis) is an important side effect of the depot injection. Oestrogen helps maintain bone mineral density in women, and is mainly produced by the follicles in the ovaries. Suppressing the development of follicles reduces the amount of oestrogen produced, and this can lead to decreased bone mineral density.
The depot injection may be associated with a very small increased risk of breast and cervical cancer.
TOM TIP: The two side effects that are unique to the progestogen injection are weight gain and osteoporosis. These adverse effects are not associated with any other forms of contraception, making them a useful fact for examiners to ask about in exams.
Problematic Bleeding
Irregular bleeding can occur, particularly in the first six months. This often settles with time. The longer the woman is taking the injection, the more likely she is to have no bleeding (amenorrhoea). Alternative causes need to be excluded where problematic bleeding continues, including a sexual health screen, pregnancy test and ensuring cervical screening is up to date.
The FSRH guidelines suggest taking the combined oral contraceptive pill (COCP) in addition to the injection for three months when problematic bleeding occurs, to help settle the bleeding. Another option is a short course (5 days) of mefenamic acid to halt the bleeding.
Potential Benefits
There are several possible benefits of the injection, with evidence that it:
- Improves dysmenorrhoea (painful periods)
- Improves endometriosis-related symptoms
- Reduces the risk of ovarian and endometrial cancer
- Reduces the severity of sickle cell crisis in patients with sickle cell anaemia
Last updated August 2020