Clarifying hormone terminology

I am writing to save myself from tearing out any more hair over the epidemic of careless use of certain terminology related to hormones. I hope you can help by printing this plea directed at your contributors and readers alike: please, please, please review your basic chemistry and pharmacology and get it straight in your minds once and for all that there is a critical difference between the word “progesterone” and words like “levonorgestrel,” “norethindrone acetate,” and “medroxyprogesterone acetate.”

You see, these aren’t just words. These are the names of different molecules with different structures and profoundly different effects on our bodies, regardless of what the pharmaceutical industry would like us to believe. I was quite mortified to read the Pediatric Pearls article entitled “Emergency contraceptive options available for adolescents.”¹ The third paragraph references “progesterone-only” emergency contraceptives and goes on to explain that “The combined pill, commonly known as the ‘morning-after pill’ contains ethinyl estradiol (estrogen) and levonorgestrel (progesterone).” I’ll grind the ethinyl estradiol–estrogen axe some other time. Right now, I need to grind the progesterone axe. If levonorgestrel and progesterone are synonymous, as the article avers, then all interested readers should ask themselves what a hormone critical for the maintenance of pregnancy (ie, progesterone) is doing in a product designed to prevent pregnancy. Levonorgestrel is a progestogen. It is not progesterone. Neither are any of the other synthetic progesterone look-alikes. The following link gives a fairly concise explanation of the difference: http://en.wikipedia.org/wiki/Progestogen.

Synthetic progestogens definitely interact with progesterone receptors, but the effects can be both weaker and stronger than that of progesterone itself, on an equimolar basis. The synthetic progesterone look-alikes also interact more strongly (compared with progesterone itself) with other receptor families, including glucocorticoid receptors and androgen receptors. These nonphysiologic interactions give rise to many of the side effects associated with synthetic progesterone look-alikes, and also contribute to the bad rap that the synthetics have vis-à-vis risk of breast cancer (when given in conjunction with estrogens). Researchers in countries outside North America² seem to understand the distinction between these various molecules (and words!). Why can’t we?

Ayn Rand once said, “A is A, reality is final and the truth is true.” Similarly, I wish that for the benefit of our patients, we in North America would learn that progesterone is progesterone, physiology is final, and the truth is that synthetic progestogens are not appropriate substitutes for our own progesterone.