In 1961 the world's first contraceptive pill went on sale in the US after several years of medical trials. The Pill works by inhibiting the release of hormones required for ovulation, in the same way as hormones produced naturally during pregnancy prevent further conception. The Pill revolutionised women's relationship with their bodies and their fertility, giving them a new sense of autonomy and control. It does not suit every woman, being unsafe for those who are prone to strokes and bloodclotting.