What causes menopause, and will progesterone interfere with this?

No, natural progesterone will not interfere with your passage through menopause (unlike synthetic progestogens used in HRT).

Briefly, menopause is the cessation of menstrual bleeding signalling that estrogen production has fallen to a very low level, preventing the build up and shedding of uterine tissue every month (menstruation). It is the mark of the end of reproduction.

The drop in levels of estrogen is due to the inability of the ovaries to manufacture the sex hormones estrogen and progesterone. A woman is never totally deficient of estrogen, although her estrogen levels drop below a point that creates monthly menstrual cycles.

Menopause is a marker of ovarian failure, because the body can no longer ripen and mature the remaining follicles into eggs for fertilisation. This happens around about age 50-55, although women are entering menopause much earlier now. It is the follicles within the ovaries that produce the vast majority of estrogen and progesterone which is produced after the ovary has popped (ovulation).

Progesterone therapy will not cause a woman to go back into monthly cycles if she has truly entered menopause because it is estrogen that creates the monthly cycles not progesterone. The build up of the endometrial tissue is under the influence of estrogen, not progesterone. And it is the drop of estrogen that signals menopause and stops your period. A woman can have stopped ovulating, and be infertile many years before her periods stop.