- A 2003 study published in The Lancet systematically reviewed 28 studies on cancer and hormonal contraceptives, including 12,531 women who had cervical cancer. The study concluded that compared with never-users of oral contraceptives, the relative risks of cervical cancer increased with long-term use.
- In 2005 the World Health Organisation classified combined oral contraceptives as a group 1 carcinogenic (cancer causing) drugs and stated that the use of combined oral contraceptives modifies slightly the risk of cancer, increasing it in some sites (cervix, breast, liver).
- A 2007 study published in The Lancet found that “Among current users of oral contraceptives the risk of invasive cervical cancer increased with increasing duration of use. The risk declined after use ceased, and by 10 or more years had returned to that of never users. A similar pattern of risk was seen both for invasive and in-situ cancer, and in women who tested positive for high-risk human papillomavirus. Relative risk did not vary substantially between women with different characteristics. The relative risk of cervical cancer is increased in current users of oral contraceptives and declines after use ceases. 10 years' use of oral contraceptives from around age 20 to 30 years is estimated to increase the cumulative incidence of invasive cervical cancer by age 50 from 7· 3 to 8· 3 per 1000 in less developed countries and from 3· 8 to 4·5 per 1000 in more developed countries.”
- A study from Thailand published in 2008 found women who had ever used or currently use oral contraceptives were almost 1.5 times more likely to develop cervical cancer than the control group. the use of oral contraceptives for longer than 3 years was significantly associated with cervical cancer. Women who had used oral contraceptives for longer than 3 years had 2.5 times increase in risk of developing invasive cervical cancer. Women who had started oral contraceptives before age 20 were almost 12 times more likely to develop cervical cancer than those who started after 20 years old.
- A 2010 study by Harvard University scientist David Hunter concluded that “Current use of oral contraceptives carries an excess risk of breast cancer. Levonorgestrel used in triphasic preparations [three different doses in a cycle] may account for much of this elevation in risk.
- Yaz and Yazmin are two common forms of hormonal contraceptive that are sold in America and the UK. Both are now known to increase the chance of blood clots. According to the FDA, around 190 women have died from blood clots. This led to a review and re-labelling of these contraceptives.
- A 2009 study conducted in Holland at 6 clinics found that currently available oral contraceptives increased the risk of venous thrombosis fivefold compared with non-use. The risk clearly differed by type of progestogen and dose of oestrogen. The use of oral contraceptives containing levonorgestrel was associated with an almost fourfold increased risk of venous thrombosis relative to non-users. The risk of venous thrombosis was positively associated with oestrogen dose.
- Two 2011 studies published in the British Medical Journal looking at data from the USA and the UK found that there was a higher risk of non-fatal venous thromboembolism in users of oral contraceptives containing drospirenone, relative to levonorgestrel users. This was consistent with the results of two previous epidemiological studies.
- Concerns about injectable hormonal contraception have arisen as a result of a number of studies showing a higher risk of HIV infection in women who are using an injectable hormonal contraceptive as a method of birth control. Not all studies have found such an increased risk. But several recent studies have: see S McCoy, et al. Oral and Injectable Contraception Use and Risk of HIV Acquisition among Women and R Heffron, et al. Hormonal Contraception Use and Risk of HIV-1 Disease Progression.
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