Combined Hormonal Contraceptives

 In Feature article, Pharmacy Information

Combined Hormonal Contraceptives (CHCs) are one of many forms of contraception available today. The term ‘Combined’ refers to the combination of oestrogen and progestogen and is the focus of this article.

While there may be circumstances where CHCs are prescribed for an indication other than contraception, it is essential that these medications are taken correctly and in the correct order. It is crucial to familiarise yourself with the patient information leaflet priory to administering (also available via, and this is also relevant to other forms of contraception and Hormone Replacement Therapy (HRT).

Types of CHC

There are different types of CHCs:

  • Monophasic – each active tablet contains a fixed amount of oestrogen and progestogen.
  • Phasic – tablets containing varying amounts of oestrogen and progestogen (the order of the strip is paramount).

Then there is an option of:

  • 21 day preparations: one tablet is taken each day in the order highlighted on the strip for 21 days followed by a seven day break (no tablets; a withdrawal bleed occurs in this period) and the cycle is repeated.
  • 28 day preparations: one active tablet is taken in the order highlighted on the strip for 28 days (the last seven days are usually placebo tablets – i.e no active ingredient; a withdrawal bleed occurs in this period) and the cycle is repeated. Exceptions to this are Zoely® and Qlaira®. The order of tablets on the strip is paramount.

How can CHCs fail?

CHC failure is possible through:

  • Administering in an incorrect order.
  • Missing a tablet/s if the ‘missed pill’ rules are not followed. Missed pill details can be obtained from the patient information leaflet or the British National Formulary (BNF). The Faculty of Sexual and Reproductive Healthcare (FSRH) has updated their guidance (also used in the BNF) to a missed pill being “one that is 24 or more hours late” (with the exception of Zoely® and Qlaira®) while manufacturers’ leaflets still refer to a missed pill as “one that is 12 or more hours late”. Therefore patients may require guidance on their options following a missed pill.
  • Vomiting and diarrhoea – recommendations in the patient information leaflet/BNF should be followed.
  • Drug interactions, such as hepatic enzyme inducers (e.g. carbamazepine, phenytoin, ritonavir, topiramate) can reduce levels of CHCs decreasing their effectiveness.

According to the latest recommendations, if antibacterials do not induce liver enzymes, then additional contraceptive precautions are not required unless vomiting or diarrhoea occurs. This should be discussed with the patient, who should also be made aware that guidance by manufacturers within patient information leaflets may differ.

Note that CHCs can interact with drugs. Lamotrigine plasma levels are reduced by oestrogens, increasing the risk of seizures if prescribed for epilepsy. Also CHCs carry a risk of lamotrigine toxicity during pill free/placebo tablet periods.

For the latest clinical guidance on the topic of contraception, please refer to:

NICE Contraception Quality Standard [QS129] –

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Professor Stephen BazireControlled Drugs