Careful observation of women taking the pill has shown that the most serious side-effects are on the circulatory system: there is an increased risk of blood clots leading to heart attacks, strokes and lung diseases. By 1980, Britain's Committee on Safety of Medicines (CSM) had received reports of 404 deaths.(1) Further studies found that 1-5% of women taking the pill have raised blood pressure.
None of these problems had been identified by animal experiments.(2) Furthermore, in some species oral contraceptives produced the opposite effect, making it more difficult for the blood to clot!(3) As Professor Briggs of Deakin University in Australia points out, "Many experimental toxicity studies have been conducted on contraceptive oestrogens, alone or in combination with progesterones. At multiples of the human dose no adverse effect on blood clotting was found in mice, rats, dogs or non-human primates. Indeed, far from accelerating blood coagulation, high doses of oestrogens in rats and dogs prolonged clotting times. There is therefore no appropriate animal model for the coagulation changes occurring in women using oral contraceptives."(4)
In 1972, the CSM described tests on over 13,000 animals which showed that very high doses of oral contraceptives cause cancer. (5) But the rats and mice used in these experiments were so susceptible to cancer that even those not dosed with the pill (the "control" animals) suffered high levels of disease: for instance, lung and liver tumours were found in 25% and 23% of control mice, and adrenal, pituitary and breast tumours were found in 26%, 30% and 99% of control rats. Under these circumstances, the British Medical Journal noted, "It is difficult to see how experiments on strains of animals so exceedingly liable to develop tumours of these various kinds can throw any useful light on the carcinogenicity of any compound for man."(5) The Journal believed the tests neither incriminated nor exonerated the pill and concluded that we would have to wait for the results of human studies.
The uncertainty of animal experiments has meant that, effectively, oral contraceptives have been tested by women themselves during long term use.
1 ) G.R.Venning, British Medical Journal, 1983, January 22, 289-292.
2) R.Heywood in Animal Toxicity Studies: Their Relevance for Man, Eds. C.E.Lumley & S.R.Walker (Quay Publishing, 1990).
3) R.Heywood & P.F.Wadsworth in Pharmacology of Estrogens, Ed. R.R.Chaudbury (Pergamon Press, 1981).
4) M.H.Briggs in Biomedical Research Involving Animals, Eds. Z.Bankowski & N.Howard-Jones (CIOMS, 1984).
5) British Medical Journal, 1972, October 28, 190.
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