Pills containing the newer types of progesterone hormones could come with a greater risk of causing serious blood clots, according to new research.
Scientists at Nottingham University have found that users of any combined oral contraceptive are at an increased risk of the serious blood clots known as venous thromboembolism (VTE) compared with non-users of similar age and health.
However, women using newer pills are around 1.5 and 1.8 times more at risk of developing VTE, than if they were using older pills. The risk is four times greater than not taking oral contraceptives at all.
Around 28% of women of reproductive age in the UK use the pill, and the researchers are keen to stress that it remains safe to take, and that newer pills generally have other advantages.
Dr Helen Stokes-Lampard of the Royal College of GPs, described the combined pill as an "excellent contraceptive choice for the majority of women".
She suggested that women already taking the pill should not change or stop their contraceptives, adding: "As with any prescribed drug, there is always the possibility of negative side effects but GPs understand the risks associated with the pill - and different generations of the pill - and will take these into account, along with medical and family history, before prescribing it to their patients.
"If women do have questions about their contraception, there is no need to panic and they should just raise these when they next visit their family planning clinic or GP surgery."