Hormonal contraception is the most effective method of controlling fertility in women.

Combined hormonal contraceptives including an oestrogen and a progestogen are the most effective for general use. They have a number of advantages, including reliability, return to fertility after treatment, low risk of menstrual problems and premenstrual tension and low risk of disorders of the ovary, breast and womb.

Low strength formulations contain 20mg ethinylestradiol, and are useful for women with risk factors for cardiovascular disease. They include Loestrin 20, Mercilon and Femodette. Standard strength formulations contain between 30 and 40mg ethinylestradiol. These are available as fixed doses, or with varying amounts of the two hormones for use at different stages of the treatment cycle. Examples include Microgynon 30, Femodene and Tri-Minulet.

Combined preparations are also available as patches (e.g. Evra), which supply hormones to the bloodstream through the skin. As with the tablet form, the first patch of a treatment cycle is important to ensure that contraceptive activity is maintained.

Side-effects of treatment with combined hormonal contraceptives include an increased risk of blood clot formation, including deep-vein thrombosis, as well as gastrointestinal problems, breast tenderness and weight changes.

Women who cannot take combination contraception due to a family history of blood clots, obesity, immobility or varicose veins can use preparations containing a progestogen, but no oestrogen, However, these are more likely to cause menstrual abnormalities, such as infrequent or very heavy menstruation. Oral preparations include Cerazette, Micronor and Norgeston, while injectable versions include medroxyprogesterone acetate (Depo-Provera) and norethisterone enanthate (Noristerat). These provide contraception for up to eight weeks.

Progestogen can also be given as a slow-releasing implant containing etonogestrel (Implanon), which provides contraception for up to three years. A progestogen-only device that is inserted into the womb is also available. It contains levonorgestrel and is marketed as Mirena. The advantage of this device is that is causes fewer side-effects and has fewer interactions with other drugs.

Side-effects of oral progestogen-only preparations include nausea, vomiting, headache, dizziness, breast discomfort and weight changes. Injections and implants can cause local reactions, including bruising and itching.

The effectiveness of homtonal contraceptives can be reduced considerably by protease inhibitors, particularly ritonavir (Norvir), atazanavir (Reyataz) and nelfinavir (Viracept), and the non-nucleoside reverse transcriptase inhibitors (NNRTIs) efavirenz (Sustiva) and nevirapine (Viramune) can dramatically reduce the blood concentrations of hormonal contraceptives^[1]. Alternative forms of contraception are required in place of, or in addition to hormonal contraception, such as condoms: these are also the best way to prevent HIV transmission during sexual intercourse.

Other drugs that may reduce contraceptive levels include rifampicin (Rifadin / Rimactane), rifabutin (Mycobutin), ciclosporin (Neoral / Sandimmun), phenytoin (Epanutin), St John’s wort, barbiturates fluconazole (Diflucan) and ketoconazole (Nizoral).

There is also a risk that hormonal contraceptives may increase a woman’s risk of acquiring HIV or speed HIV disease progression, although further research is required.