The pill has been described as the most significant medical advance of the 20th century.
Hailed as playing a major role in the women's liberation movement, it was associated with the swinging sixties and greater sexual freedom.
But it has caused much controversy over its short life span due to health scares and concerns about teenagers taking the pill.
Introduced in the UK in 1961 for married women only, it is now used by 3.5 million women between the ages of 16 and 49.
That means that a quarter of this age group are using the pill, which now comes in 32 different forms.
Developed by American biologist Dr Gregory Pincus, the pill works by suppressing ovulation.
Tested in the 1950s on Puerto Rican and Haitian women, the first version of the pill contained the hormones oestrogen and progestin, which were synthetically produced to mimic the body's natural hormones.
Take-up of the pill was fast. Between 1962 and 1969, the number of users rose from approximately 50,000 to one million.
In the USA, around 1.2 million women used the pill withing two years of its launch in 1960.
Now the number of users is around 11 million.
Worldwide, around 100 million women take the pill.
http://news.bbc.co.uk/1/hi/health/250337.stm