For me the major **clinical** difference in the bioidentical HRT is the progesterone/progestagin. This is because it may be where the breast cancer risk lies.
Oestradiol is available in both traditional and bioidentical paradigms. It is the same as the oestradiol molecule our bodies make premenopause. So the oestrogen available in the traditional HRT can be bioidentical as well. It can be a patch or a tablet. In the bioidentical world this can be accompanied by the other two oestrogen molecules that our bodies make. It can be given as a cream or lozenge in the bioidentical world. This latter combination is not available in the traditional model. It is unclear if all three are necessary clinically. There are other oestrogen like medications available in the traditional HRT which are not the same as our bodies make. It is unclear if this is a bad thing or not but personally I cant imagine why anyone would chose to take an analogue rather than the oestradiol.
I personally use a prescription oestradiol patch 50 mcg.
Now the progesterone. Here's the rub. In the women's health study it appeared to be the addition of progestogen/progestagin that increased the risk of breast cancer. However they did not separate progesterones (same as our bodies make) from artificial progestagins. It may be the latter that is the culprit, but it is unclear. Here again, I personally would not take the latter. Bioidentical micronised oral progesterone capsules are available both in the traditional model and the bioidentical model. Or as a cream but I would be loath to bet my endometrial protection on the variable absorption of a cream. In some countries it is available as a patch in combination with oestradiol. Or there is an option of a Mirena which I personally have as progesterone makes me feel very drowsy all day.
The word bioidentical is thus a very clever marketing word. The same molecules are available in the traditional medical model as well.