Please note: This archive was last updated in 2005.

RHO archives : Topics : Contraceptive Methods

Injectables

Overview

Injectable contraceptives contain synthetic hormones that are administered by deep intramuscular injection. Injectables are a safe and effective method of reversible contraception for most women (IFFP 1999). Two types of injectable contraceptives are available: progestin-only injectable contraceptives and combined injectable contraceptives that contain both a progestin and an estrogen hormone. Available progestin-only injectables include DMPA (depot medroxyprogesterone acetate) and NET-EN (norethindrone enanthate). Available combined injectables are Cyclofem™ (also called Lunelle) and Mesigyna .

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Characteristics of injectable contraceptives

Effectiveness

Progestin-only injectables: 0.1% to 0.6% failure rate during first year of use. Combined injectables: 0.2% to 0.4% failure rate during first year of use.

Age limitations

No general restrictions on use based on age for combined injectables; progestin-only injectables not recommended for girls younger than 16 because of theoretical concern about the effect on bone density.

Parity limitations

No restrictions on use.

Mode of action

Primarily by thickening cervical mucus, thereby preventing sperm penetration, and by inhibiting ovulation.

Effect on STI risk

Not protective.

Drug interaction

Use of certain antiseizure medications (barbiturates, carbamazepine, phenytoin, primadone) and antibiotics (Rifampin and Griseofulvin) may reduce the contraceptive effect of injectables .

Duration of use

Most women can use injectables safely throughout their reproductive years (if the woman is satisfied with the method and has no problems with it).

Return to fertility

After a delay of about three to six months for progestin-only injectables; within three months for combined injectables.

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Key issues

DMPA and Cancer

Although injectable contraceptives were developed shortly after COCs, political controversy has limited their availability until recently. DMPA (known widely under the brand name Depo Provera) has been the most widely studied injectable contraceptive. Recent research by the World Health Organization has allayed much of the fear about DMPA and cancer. According to a nine-year WHO study, DMPA did not increase women's overall risk of breast cancer, invasive cervical cancer, liver cancer, or ovarian cancer, and it decreased the risk of endometrial cancer. Women may face a slightly increased risk of breast cancer in the first five years after they start DMPA, perhaps due to accelerated growth of existing tumors (PATH/Outlook 1992; Lande 1995). These studies and the 1992 approval of DMPA in the United States has helped pave the way for increased use of both progestin-only and combined injectable contraceptives (PATH/Outlook 1992).

DMPA and Bone Mass

Studies on the effects of DMPA on bone mineral density have been controversial. However, one recent study on the effect of DMPA on bone mineral density seems to offer reassurance regarding long-term use of the drug. Results of a longitudinal cohort study of 59 Chinese women have led its researchers to conclude DMPA can be used on a long-term basis without fear of linear bone loss leading to early osteoporosis. Over a three-year period, the annual rate of bone loss at three sites (lumbar spine, neck of the femur, and the Wards triangle) was significantly less than projected values, and the duration of DMPA use was not significantly related with the rate of bone loss (Tang 2000). An interesting review of hormonal contraceptives and bone mass is presented in the IPPF Medical Bulletin (Meirik 2000). In this article, Dr. Olav Meirik concludes that the long-term effects of hormonal contraceptives on bone mass are dependent on age and the life cycle. For women in the middle years of their reproductive lives, bone-mass changes resulting from hormonal contraceptives are small and transient. In adolescents, however, DMPA in particular does seem to slow the accumulation of bone mass. It is not yet known whether this is a transient effect.

While the effects of DMPA and levonorgestrel implants on the bone mass of women in perimenopause have not been well studied, two recent studies shed some light on these issues. A study on the effect of DMPA on bone mass in women aged 30-45 years did not find that DMPA accelerated bone loss during this stage of life. For those DMPA users who did experience high bone loss early in the study, some—but not all—successfully used estradiol or calcium to reduce bone loss (Merki-Feld 2003). The second study evaluated early menopausal bone loss among women who had used DMPA through menopause compared to a control group who reached natural menopause and did not undergo hormone replacement. The DMPA group showed little change in bone mineral density during the three-year study compared to the control group, which showed rapid loss of bone density. The authors conclude that women who use DMPA through menopause have less severe rates of bone loss from lumbar spine and femoral neck, possibly because they have already lost the estrogen-ensitive component of bone (Cundy 2002).

DMPA and STI Risk

Worldwide nearly 150 million women use hormonal contraception. Use of progestin-only injectables, primarily DMPA, is high in some areas of the world where HIV prevalence is high. The relationship between hormonal contraception and acquisition, transmission, and progression of STIs—including HIV—continues to be an important area of research (FHI 2003; FHI 2001). Research results are conflicting for a variety of reasons, but it is clear that hormonal contraceptives do not protect against STIs or HIV. Providers should counsel women who use injectable contraceptives to use a condom during each act of intercourse to protect against STI or HIV infection.

Recently announced results of a study in the United States found that women who used DMPA appear to have a three-fold increase in risk of acquiring Chlamydia and Gonorrhea infection when compared to women not using hormonal contraception (MAQ 2004). While the study results should be taken seriously, the study sponsors do not call for changes in provision or use of DMPA. It is important to note that there is no increased risk of infection for women who are in monogamous relationships with uninfected partners. Reproductive Health Technologies Project has issued a brief discussing the findings from this study (RHTP 2004).

Safe Injection Practices

Where available, auto-disable (AD) syringes and sharps disposal containers can improve injection safety for family planning clients, health workers, and communities by reducing reuse of needles and preventing needlestick injuries (PATH/USAID 2001).

For More Information

Please see the references listed in the Annotated Bibliography or the section on new injectables in the Contraceptive Research and Development page. Also see Hormonal Contraception, IUDs, and HIV Risk.

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