From what I have looked at, Mirena gives the least systemic progesterone, but it is still quite a bit.
The next lowest is the old progestogen only pills, then the newer sort (like Cerezette). This changes the lining, mucus etc to prevent conception and cerezette may be enough to prevent ovulation at times.
Then hrt (quite a lot is required to be sure that it does its job with the oestrogen effects on the uterus).
Then the combined pill - which is quite a lot of progestogen! I used to think that was because of the higher oestrogen, but the levels in the coc are not all that high compared to a natural cycle. It is used in conjunction with the oestrogen to shut down the normal cycle and prevent ovulation from happening.
I tried comparing all the pills and preparations that contain levenorgestrel as it is used across the preparations (different progestogens need different amounts). However, pills have to be absorbed through the gut into the blood, then it passes through the liver, where a lot is taken out - so they have to be of a sufficient dose to get over this (and also designed to prevent this - hence the synthetic
progestogens/progestins rather than natural progesterone, which needs to be
micronized. ) The blood levels will go up and down on a daily cycle as you take the pills. This should not happen with mirena because should be releasing the hormone more evenly with less of the liver effect.
I too await Hurdity's researches. I am pretty sure that it is less than the progestogen only pill, but a bit higher than you would think.
(I gave up trying to work out patches

)
(Also not heard about hair loss with oestrogen - personally, having been on the combined pill for years, I would think the addition of oestrogen would help with a lot of things - I had effects on the progestogen only type that I never noticed on the combined.)