The progesterone creams and gels can be effective to protect the womb as long as monitored with scans. I believe MaryG uses a gel and has clear scans.
Yes, that's right dangermouse.
To be clear, I'm currently using progesterone gel every day alongside 75mcg Cerazette. The progesterone gel is produced by the same manufacturer as my Oestrogel (Oestraclin) and I was able to get approximately 50mg progesterone per day from it which is OK for one pump of gel and my uterine scans were always way below 5mm. I used to occasionally bolster it up with 50mg vaginal Cyclogest but not very often.
I have now had to add in the Cerazette because I needed to increase my Oestrogel to two pumps to prevent my brain stem auras - this migraine sub-type is caused by low oestrogen levels. By keeping the Cerazette to a minimum and continuing with the progesterone gel I'm managing well with no side effects, not even breast pain. I could have used Cyclogest @50mg every day but it's a bit messy and taking a pill is easier.
I have used compounded progesterone lozenges in the past (see my thread in the Alternative Therapies section) and they was excellent. It's expensive but it works. It comes as a buccal lozenge, sublingual drops or a transdermal cream. I didn't have any side effects at all and once again, uterine scans were usually about 3mm. I would have continued with the compounded progesterone but Brexit meant they could no longer post it to an EU state.
I think the NHS over prescribe progesterone, probably because they don't routinely scan women unless they have a problem. I think they worked out the minimum amount that works and then doubled it.