Hi Alora,
I have asked two different endocrinologists for a prescription for progesterone and both have declined. There are many on this forum who have anecdotal experience with it, and most of them seem positive, but that is not clinical evidence, and that's what doctor's tend to want.
For example, one of the very few articles I could find:
Clinical Review: Breast Development in Trans Women Receiving Cross-Sex Hormones
The Journal of Sexual Medicine
Volume 11, Issue 5, May 2014, Pages 1240–1247
The aim of this study is to assess the effect of cross-sex hormone therapy on breast development in adult trans women. Additionally, we aimed to investigate the benefit or harm of administration of progestogens on breast development. Only few studies with low quality of evidence addressed these topics. The available evidence suggests that breast development is insufficient for the majority of trans women and that type and dosage of hormonal therapy seem not to have an important role on final breast size.
Conclusions
Our knowledge concerning the natural history and effects of different cross-sex hormone therapies on breast development in trans women is extremely sparse and based on low quality of evidence. Current evidence does not provide evidence that progestogens enhance breast development in trans women. Neither do they prove the absence of such an effect. This prevents us from drawing any firm conclusion at this moment and demonstrates the need for further research to clarify these important clinical questions.
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But there are tons of articles like this:
Minireview: Progesterone Regulation of Proliferation in the Normal Human Breast and in Breast Cancer: A Tale of Two Scenarios?
By: Hilton, Heidi N.; Graham, J. Dinny; Clarke, Christine L.
MOLECULAR ENDOCRINOLOGY Volume: 29 Issue: 9 Pages: 1230-1242 Published: SEP 2015
Progesterone (P), which signals through the P receptor (PR), is critical in normal development of the breast, but its signaling axis is also a major driver of breast cancer risk. Here we review recent advances in the understanding of P signaling in the normal human breast, with a focus on the importance of the balance between autocrine and paracrine signaling. To date, most data (which derive largely from mouse models or human breast cancer cell line studies) have demonstrated that the vast majority of PR+ cells appear to act as "sensor" cells, which respond to P stimulation by translating these hormonal cues into paracrine signals. However, growing evidence suggests that, dependent on the cellular context, P may also signal in an autocrine manner in a subset of cells in the normal mouse mammary gland and human breast. It has been suggested that it may be dysregulation of this autocrine signaling, resulting in a "switch" from a predominance of paracrine signaling to autocrine signaling in PR+ cells, which is an early event during breast tumorigenesis. This review summarizes current evidence in the literature that demonstrates the mechanisms through which P acts in the normal human breast, as well as highlighting the important questions that remain unanswered.
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Progesterone also has important effects on the CNS, as it is metabolized to allopregnanolone, and important neuro-protective steriod that has anti-depressant activity. The main biological role of progetins is on the uterus, which is why many doctors discount using them as part of an HRT regimen for transsexuals.
Here is another article summary you may find useful:
Int J Fertil Womens Med. 1999 Mar-Apr;44(2):96-103.
Uses of progesterone in clinical practice.
Warren MP1, Shantha S.
Progesterone is the natural progestagen produced by the corpus luteum during the luteal phase. It is absorbed when administered orally, but is greater than 90% metabolized during the first hepatic pass. This greatly limits the efficacy of once-daily administration and also results in unphysiologically high levels of progesterone metabolites, particularly those reduced at the 5-a position. These metabolites can cause dizziness and drowsiness to the point of preventing the operation of a motor vehicle.
Synthetic progestins, such as medroxyprogesterone acetate and norethindrone acetate (NETA), have been specifically designed to resist enzymatic degradation and remain active after oral administration. However, these compounds exert undesirable effects on the liver and often cause severe psychological side effects. The permeability of the skin does not allow for administration of progesterone in the quantities normally produced by the corpus luteum, i.e., up to 25 mg/day during the mid-luteal phase.
To avoid this problem, synthetic progestins such as NETA have been administered transdermally. These compounds, though, just like synthetic estrogens administered non-orally, retain undesirable hepatic effects even when administered transdermally. Transvaginal administration of progesterone is a practical non-oral route available for administering progesterone. Early experience was gained with vaginal suppositories, which lack manufacturing controls.
Recently, a new progesterone gel formulation has been designed for vaginal use. The clinical acceptability of this product has been enhanced by the bioadhesive characteristics of its polycarbophil-based gel, which conveys controlled and sustained-released properties. Investigations have shown that because of local direct vagina-to-uterus transport, which results in a preferential uterine uptake of progesterone, this formulation given in conjunction with physiological amounts of estradiol produces endometrial changes similar to those seen in the luteal phase, despite plasma progesterone levels that remain subphysiologic. Studies in infertility show that vaginal progesterone in this form allows secretory transformation of the endometrium and the development of pregnancy despite providing low systemic progesterone concentrations. Fewer side effects occur when used for hormone replacement than typically encountered with progestins and oral progesterone. Uses in patients with infertility and hypoestrogenism and secondary amenorrhea are reviewed.
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As you can see, it's not a straightforward issue, even when being used by natal women.
~Terri
