#Because they block Gn-RH receptors

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OKOK i love this so much and i want to actually explain some of the biology thats going on here cuz finally i found a tumblr post that has to do with my special interest! There isn’t much actual research on this area of trans health and im by no means an expert on this at all so please take what I say with a grain of salt :p

So basically- most people, regardless of sex, produce gonadotropins (type of hormones) from the pituitary gland in their brain. There are two types of gonadotropins: FSH (Follicle Stimulating Hormone) and LH (Leutinizing Hormone). These are the hormones responsible for starting the menstrual cycle by 1) stimulating the follicles in the ovaries to start growing eggs (courtesy of FSH) and 2) getting the mature egg to ovulate (courtesy of LH). For males, these hormones have different jobs: stimulating the seritoli cells in the testes to produce ABP aka Androgen Binding Protein (courtesy of FSH), and stimulating the leydig cells to produce testosterone (courtesy of LH) (also this is the primary source of natural testosterone in males); and then these substances bind together (testosterone is a type of androgen or male sex hormone which binds to ABP like the name suggests) in order to begin producing sperm.

However, when a trans woman takes testosterone blockers, the cells’ testosterone receptors are blocked and the binding cannot happen, at least not as much— which is why sperm production often decreases or stops entirely while on HRT. Plus, with feminizing replacement hormones, testosterone production (typically initiated by LH) starts to go down and estrogen + progesterone goes up, and now you start to see a hormone cycle that looks more similar to that of a cis woman.

Normally, when you have a uterus and a menstrual cycle, estrogen and progesterone are (mostly) produced in the ovaries throughout the egg-growing process: estrogen is produced by the developing follicle (which is growing the egg) and progesterone is produced by the Corpeus Luteum, aka the broken remains of the follicle after it ovulates and the egg bursts out of there. Throughout the egg-growing process, the follicle continues producing more and more estrogen, which travels to the brain and basically serves as a meter to track the progress of the egg’s growth (technically theres multiple eggs growing at once and only the most mature egg gets ovulated but i wanna keep things simple for this explanation) and once estrogen levels reach a certain high point thats what triggers the release of LH and causes ovulation— resulting in the Corpues Luteum from the remains which begins producing a bunch of progesterone. Both estrogen and progesterone serve to prepare the inner lining of the uterus for the implantation of a fertilized egg— estrogen starting that process during egg development and progesterone continuing that process after ovulation (as well as some extra stuff for the benefit of the potential fetus).

Period cramps in general have not been studied enough so we don’t know everything but the working consensus for your typical period cramps are that they are caused by prostaglandins— hormone-like substances produced by most organs and tissues all throughout the body with a wide range of effects, inculding to help shed the uterine lining during a period by binding to natural prostaglandin receptors in the uterus and causing contractions (they are released by the uterine lining itself in response to a drop in progesterone after the fertile window passes and the Corpeus Luteum degenerates). This is the same process that causes contractions during labor and its why the feelings are often described as being similar (albiet one far more painful than the other in most cases lol). This is also why ibuprofen works against cramps, since they block the prostaglandin receptors.

Thats not the only way or time you can get period cramps though. Some people get certain physical and/or emotional symptoms before their actual bleeding starts due to the hormonal processes i described earlier during the egg developing process. Remember the estrogen and progesterone i mentioned that peaks when the egg becomes fully matured and ovulates? Well estrogen, as you probably know, causes swelling of the breasts, and thats why some people can have bloated, tender, or tight/painful breasts for a bit before their period. And thats only one the potential symptoms of these various hormonal fluctuations; there’s loads others, both physical and emotional, such as cravings, anxiety/depression, loss of appetite, fatigue, acne, lack of concentration, irritability, nausea, the list goes on and on and includes, yes, ✨cramps.✨

This is called Premenstrual Syndrome, or PMS. You’ve probably heard of it before, and if youve gone through it you probably know what it feels like. Not everyone experiences it and even those who do don’t experience it all the time, but it makes sense that trans women on HRT would be able to. Despite not having ovaries where most estrogen and progesterone would normally come from, as long as someone gets those hormones from somewhere else (HRT) they pretty much have everything else they need already in their bodies. When cis women get hysterectomies they often still have their ovaries— the source of their estrogen and progesterone— so they still have PMS symptoms and cycles despite not having periods. We don’t know much about this in trans women. There has not been anywhere close to enough research. But with the influx of estrogen and the blocking of testosterone it makes sense that the body would adapt and begin the cycles it was made to do based on the hormones available, just like cis women do without a functioning uterus. Afterall its not like the replacement hormones from HRT would remain static and consistent, we have hormonal regulatory systems (pituitary gland) for a reason. I just think its so amazing and beautiful how all of this fits together. How when you really take a look at reproductive biology, the sex your assigned at birth just melts away.

Literally had cramps while drawing this