So sorry you're still suffering Niamh.
From what I've read, it's a daily dose of 4 pumps which surpress ovulation. I think it says this on Studd's website and the NAPs site (association for PMS). If you want to stop the fluctuations then you need to stop the ovulation.
But I do think that HRT is a bit like trying to pin the tail on the donkey, especially when your psychological symptoms are severe.
But on Studd's website, reading his case studies, all the women on there used high dose HRT and saw a huge improvement by the end if the very first cycle of HRT.