I think the main reason for this is that the first POP/mini-pills had to be taken within a window of 3 hours each day, so it was quite easy to miss this and be at risk of pregnancy. These pills are still available and work well for lots of women, however, the most commonly prescribed POP these days are ones which contain a hormone called Desogestrel (e.g. Cerazette, Cerelle, Zelleta). These POP have a longer window, 12 hours, which makes it much easier to take in the right time frame. As a result prescription of POP is becoming much more common – 10 years ago only about 20% women using oral contraception were taking POP while these days it’s more like 40%. The combined pill still has a longer window period, 24 hours.
Although there are some more risks with the combined pill, for most healthy people these are very low and generally outweighed by the benefit of preventing pregnancy. It would be interesting to hear if anyone has had experience switching from the combined pill to POP or visa versa and how you found it?