I had to swap to progesterone only due to suddenly being told the combined pill was no longer an option (like many I had been happily on the combined pill with no negative effects for over 10 years). I was very dubious to go on this, I constantly bled for 2 months and then it became more irregular but generally every month somehow I would have a period. The main reason I asked to change was due to the effect on my mood. It was only coming off this that I realised how low it made me.
Hard for me to know as moved onto nother progesterone only pill but definitely improved mood
Cycle return to normal