Benefits, side effects & risks
Benefits
CHC use can help with menorrhagia and dysmenorrhea. There is some evidence to suggest that it can help with premenstrual syndrome. It reduces the risk of recurrence of endometriosis, particularly if taken without hormone free interval (HFI), and has a role in tackling acne, hirsutism and menstrual irregularities associated with PCOS. Its usage appears to reduce the risk of endometrial, ovarian and colon cancer.
Side effects
Breakthrough bleeding is a relatively common problem for users of CHC and estimated to be 10-18%. It seems to happen more in the first 3 months and may settle. For those women that continue to have problems with irregular bleeding, research suggests changing to a second/third generation progestogen, increasing the dose of estrogen (eg 30mg) or extended/continuous regimens may help.
Other side effects attributed to CHC include headaches, nausea, dizziness, bloating, breast tenderness and mood disturbance (though trials have shown similar rates of reporting in placebos). If a woman is troubled by these symptoms, changing the type of CHC (different progestogen, lower estrogen) may help.
For those women experiencing side effects during their hormone free interval (HFI), reducing the frequency or length of HFI may help. This can be done in a variety of ways: 1) back to backing packets for 3 months before HFI, 2) reducing HFI to 4 days rather than traditional 7 days, 3) continuous use with no breaks or 4) a tailored regime of continuous use (at least 21 days) until breakthrough bleeding and then having HFI for 4 to 7 days. This applies to all CHC, including vaginal ring and patch.
Risks
Use of CHC increases the risk of venous thromboembolism (VTE) by 3-3.5 fold. This risk is highest when first started or restarted and so frequent stopping and restarting should be discouraged. The absolute risk, however, remains low, estimated to be between 5 and 12 per 10,000 women per year taking the CHC compared with 2 per 10 000 non-CHC users per year. 1% of these will be fatal. Characteristics and medical conditions that increase a woman’s risk (such as increasing age, higher BMI, postpartum and thrombophilia should be considered before starting CHC. These are laid out in UKMEC 2016 guidance. Both the type of progestogen and strength of estrogen can affect the relative risk of VTE, with 3rd generation progestogens and higher dose EE having higher risk.
High altitude can increase erythropoiesis and so increase the risk of VTE. It is recommended that women spending more than a week above 4500m should consider an alternative method of contraception. Due to a theoretical risk of increased risk of VTE on long haul flights with CHC users, it is recommended that women keep periods of immobility to a minimum and stretch legs/walk as much as possible during the flight. GDG does not currently recommend antiplatelets or compression stockings. CHC should be stopped 4 weeks prior to any major surgery or expected prolonged immobility to reduce VTE risk. Due to metabolic and weight changes with pregnancy, VTE risk is also increased in the postpartum period. For women within 3 weeks of giving birth, CHC is best avoided. For women berween 3-6 weeks postpartum, safety depends on other risk factors for VTE (including breastfeeding, see UKMEC criteria for full details).
Use of CHC increases the risk of myocardial infarction and stroke but absolute risk remains very low (1 and 2.1 per 10,000 woman years of CHC respectively). Risk is increased with increasing dose of estrogen. There appears to be no difference in risk of arterial disease between different progestogen groups. Women with significant risk factors for arterial disease should avoid CHC. UKMEC 2016 cautions/suggests avoid use in women over 35 years, who smoke, are hypertensive, have diabetes, and those with dyslipidaemia. Women with migraine with aura (UKMEC 4), or new onset migraines (UKMEC3) are also advised to avoid CHC. It is inadvisable for women to continue taking CHC after the age of 50 due to the increased risk.
CHC use increases the risk of breast cancer (relative risk of 1.19). This risk reduces slowly over time after stopping CHC (back to baseline within 5 years of stopping). For women with genes BRCA the risk of breast cancer is likely to be slightly increased with CHC use; paradoxically the use of CHC will reduce their risk of ovarian cancer. There is a small increased risk of cervical cancer (relative risk of 1.89) for CHC users of 5 or more years. This risk returns to baseline after 10 years from stopping CHC.
Like many forms of hormonal contraception, CHC metabolism may be affected by enzyme inducers and therefore should not be co-prescribed (see Box 3 for drug interactions).