Mechanism of action

The COCP prevents conception by acting on:

• The hypothalamic-pituitary-ovarian axis to suppress synthesis and secretion of follicle-stimulating hormone and the mid-cycle surge of luteinising hormone, thus inhibiting the development of ovarian follicles and ovulation.
• Cervical mucus to prevent penetration of sperm.
• The endometrium to inhibit blastocyst implantation.

Efficacy

The efficacy of any contraceptive method depends on the protection afforded by the technique itself and how consistently and correctly it is used.

The failure rate for the COCP (when used perfectly) is estimated to be only 3 pregnancies per 1,000 women per year. However, the typical failure rate is closer to 90 pregnancies per 100 women per year.^[3] 

The efficacy of the COCP may be decreased by severe vomiting or diarrhoea and concurrent use of other enzyme-inducing medications.

What to do before starting the combined oral contraceptive pill

To ensure that the woman fulfils the criteria of eligibility for use:^[1][4]

• A full clinical history must be taken:
  • Current and previous medical conditions.
  • Drug use, including prescription, over-the-counter and herbal remedies. The COCP is not usually recommended in women on lamotrigine monotherapy, due to the risk of reduced seizure control whilst on it and the potential for toxicity in the pill-free week.^[5]
  • Family history.
• Specifically, enquire about migraine and cardiovascular risk factors (smoking, obesity, hypertension, thrombophilia, previous venous thromboembolism (VTE) and hyperlipidaemia).
• The patient's preference and individual concerns about the COCP must be addressed - for example, there is no evidence of weight gain associated with COCP use.^[6] Be mindful of ethnocultural issues.
• Record blood pressure and body mass index (BMI).

The patient should be aware that:

• There is a very small increased risk of breast cancer associated with use, but this is reduced to no additional risk 10 years after stopping the COCP.
• There is also a small additional risk of cervical cancer that increases with extended duration of use.

Contra-indications

Ensure that none of the following applies to the patient:^[1]

• Women aged over 35 years who smoke are NOT recommended to take the COCP. There is a very small increased risk of myocardial infarction (MI) with current COCP use in nonsmokers, which increases further in smokers. Women aged over 35 years, who have stopped smoking for more than one year, may be considered for use.
• Women with a BMI over 35 have an increased risk of MI and VTE, and risks of use outweigh benefits.
• Women who have blood pressure above 140 mm Hg systolic and/or above 90 mm Hg diastolic should not use the COCP.
• Women with a personal history of VTE, or who are known to have a thrombogenic mutation, should not use the COCP. A thrombophilia screen should NOT be routinely performed before prescribing. If a thrombophilia screen is done any results should be interpreted with a haematologist.
• Women who have had migraine with aura should not use the COCP. Women aged over 35 years with migraine, but no aura, should not use the COCP.

If the patient is at risk of sexually transmitted infections, advise about continuing use of a barrier method, eg a condom for protection.

Interactions

Consider whether any of the following apply to the patient:

• Liver-enzyme inducers such as carbamazepine, phenytoin and rifampicin accelerate the metabolism of oestrogen and progestogen and may reduce the efficacy of hormonal contraceptives (see separate article Contraception and Special Groups):
  • Apart from the very potent enzyme inducers rifampicin and rifabutin, women who are on an enzyme-inducing drug and who do not wish to change from the COCP may increase the dose of COCP to at least 50 micrograms ethinylestradiol (EE) (maximum 70 micrograms) and use an extended or tricycling regimen with a pill-free interval of four days.
  • In women using enzyme-inducing drugs with the COCP, breakthrough bleeding may indicate low serum EE concentrations. If other causes (eg chlamydia) have been excluded, the dose of EE can be increased up to a maximum of 70 micrograms EE.
• The bioavailability of drugs such as theophylline and ciclosporin is increased by the COCP and may have toxic effects.

Advise the patient that:

• Recent advice from the Faculty of Sexual and Reproductive Healthcare is that additional contraceptive precautions are not required during or after short courses of antibiotics that do not induce enzymes.^[5]
• Long-term, non-enzyme-inducing antibiotics also do not require additional protection.

Administration

Take time to explain that the COCP is taken for 21 consecutive days, at approximately the same time of day (mobile phones can also act as alerts/alarms). This is followed by seven pill-free days (or seven days of neutral tablets) to allow endometrial shedding and a withdrawal bleed. Contraception is still provided during the hormone-free interval.

• Ideally, the COCP should be started on the first day of menstrual bleeding, but can be started up to day five without the need for extra protection.
• It can be started at any other time IF THE PATIENT IS SURE SHE IS NOT PREGNANT, but additional protection, eg condoms/abstinence, will be needed for the first seven days.^[7] If the patient is quick-starting after ulipristal acetate emergency contraception, extra protection is required for 14 days.

Give advice on missed pills:^[8]

• Advise that the leaflet in the packet contains specific recommendations, but that missing one pill, at any time, does not compromise contraception.
• If vomiting occurs within two hours of taking the COCP then another should be taken as soon as possible.

Extended cycling

The patient should be informed that avoidance of bleeding can be managed by extended or continuous administration of the COCP:

• It has become popular for the treatment of endometriosis, dysmenorrhoea and menstrual-associated symptoms.^[9]
• Women may be given the option of 'tricycling' packets of pills to avoid menstrual periods, for reasons of personal choice.
• Women are likely to report less and lighter bleeding with reduced menstrual pain and bloating.
• Similar rates of breakthrough bleeding are found with single or extended cycling.

Non-contraceptive benefits

Patients may also be interested in using the COCP for:

• Reduction of menstrual pain and bleeding.
• Reduction in incidence of functional ovarian cysts.
• Reduction in risk of ovarian and endometrial cancer.
• Reduction in risk of colorectal cancer.
• Improvement in acne vulgaris.^[10]

Choice of preparations

The woman may have a particular brand she has heard of, or had recommended by family/friend. If not, or it is unsuitable, consider:^[11]

• A suitable first choice which is a monophasic preparation with 30-35 micrograms ethinylestradiol (EE) and low-dose norethisterone or levonorgestrel.
• A preparation with the lowest oestrogen and progestogen content, which is able to provide adequate cycle control (less breakthrough bleeding) with minimal side-effects, should be used for each individual.
• The choice of progestogen is likely to be the most important factor in cycle control and third-generation pills may be considered at follow-up for those with unacceptable side-effects from other progestogens.
• Low-dose oestrogen pills, eg Loestrin®, Mercilon® and Femodette® are particularly appropriate for women with risk factors for circulatory disease, or who have a lower risk of conceiving through natural decline in fertility, eg the mature woman.

Dianette®

Dianette® is used where acne or moderately severe hirsutism is a problem. It should be withdrawn if there is no improvement after three months of use. It carries a four times higher risk of VTE than other COCPs and should not be used indefinitely.

Follow-up

• Ideally, follow-up should be after three months, but advise the patient to come sooner if she becomes concerned. Provide information on signs that should prompt medical opinion eg new headache or VTE.
• Women should be encouraged to persist for three months before considering an alternative.
• Repeat blood pressure measurement, and document the results.
• Enquire about adverse effects or problems.