In a comparison study of the effectiveness of different contraceptives in the UK, the below table shows that the contraceptive pill in all forms available are of equal effectiveness:

  Percentage of women experiencing an unintended pregnancy within the first year of use
Typical use Perfect use
Combined oral contraceptives’ 9% 0.3%
Progesterone-only pill 9% 0.3%


The above information has been taken from NICE (National Institute for Health and Care Excellence). View the full assessment here. [link]