The CSM have provided evidence that the risk of venous thromboembolism associated with oral contraceptives containing norethisterone, levonorgestrel or ethynodiol increases the risk (excess risk) of venous thromboembolism by around 10 to 15 cases per 100,000 women per annum. However these studies showed that combined oral contraceptives containing desogestrel and gestodene are associated with an approximate two-fold increase in the risk, compared with those containing other progestogens.
Insufficient data was available to know whether there was an increased risk associated with combined preparations containing norgestimate.
The National Prescribing Centre have stated that (1):
- all COCs increase the risk of venous thromboembolism (VTE). There is a small excess risk associated with COCs containing desogestrel or gestodene. However, in absolute terms, the risk is still low and is lower than the risk of VTE in pregnancy
- on a population level, it would seem sensible to prescribe COCs that do not contain desogestrel or gestodene first-line. However, on an individual level, providing women are fully informed of the risks and do not have medical contraindications, it should be a matter of clinical judgement and personal choice as to which type of oral contraceptive is prescribed
- all COCs should be prescribed with caution to women with a higher baseline risk of VTE
- the riisk of VTE associated with COC use and non-use is detailed in the table below:
|Circumstance||Risk of VTE per 100,000 women|
|Healthy, non-pregnant women (not taking any oral contraceptive)||About 5 cases per year|
|Women taking COCs containing levonorgestrel||About 15 cases per year of use|
|Women taking COCs containing desogestrel or gestodene||About 25 cases per year of use|
- MeReC Bulletin (2006); 17(2):1.
- BNF 7.3
- Waller P (1995). Venous thromboembolism and oral contraceptives that contain desogestrel or gestodene. CMO's Update; 8: 2.
- Medical Monitor (14/4/99): 13.