Clarification about Monotherapy with Either CPA, MPA, spironolactone or the 'Mides and Safety
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shrouded_reflection via
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Loss of bone density is due to low estrogen levels (or in the case of men low testosterone levels, as testosterone is aromatized into estradiol), so as long as whatever your medication is doesn't result in low functional levels of both of those hormones you don't have any issues with density loss. In the short term it doesn't matter too much, and the body can bounce back from small periods of loss, but in the long run you need to maintain adequate hormone levels or risk early onset osteoporosis and other similar conditions.
Finasteride only blocks DHT production, and since DHT can't be aromatized to estradiol then it shouldn't have any impact on T or E levels, so no change in bone density. I would assume a similar effect with Dutasteride, but it's a drug I'm less familiar with.
For progestins such as CPA, MPA, you are downregulating the hypothalamic–pituitary–gonadal loop, which results in reduced T and E production. Supplementation with hormones is required in the long run.
Bicalutamide does seem to have slight estrogenic effects, however it isn't sufficient to offset the loss of estrogen via aromatization when it comes to bone density. spironolactone also falls into this category. Either way, estradiol supplementation is needed if your body doesn't already produce it in significant quantities.
Raloxifene can be used as an estrogen replacement in conjunction with an AA if for some reason the full effects of estrogen are not desired (raloxifene does not activate estrogen receptors in breast tissue). However it is not as effective at maintaining bone density and has a number of potentially serious side effects in the long run, so should be considered only a method of last resort, such as for non binary individuals who can't get a mastectomy.