Progestin/progesterone reducing bruxism & hyperprolactinemia

In a small sample size study (n=33) of postmenopausal women the addition of a Progestin, particularly Medroxyprogesterone, reduced the incidence of bruxism to zero from 11.1%. Both low and very high Progesterone (P4) levels are associated with the incidence of bruxism in premenopausal and pregnant women, respectively. Even with rectal P4 it's imposible to reach pregnancy levels of P4. So the issue is low P4.

In this scenario we are analogous to postmenopausal women because Testosterone is the dopaminergic hormone that controls muscle movement.

The etiology of hyperestrogenic/hypoandrogenic induced bruxism is VMAT2 downregulation in dopaminergic neurons in the prefrontal cortex and more importantly the striatum. A hyperdopaminergic striatum can also cause bruxism, hence very high levels of P4 also produce bruxism.

Accordingly to it's dopaminergic effect P4 also reduces Estradiol induced hyperprolactinemia.

TLDR: Progesterone can protect against some side effects of Estradiol.