The optimal dose of any hrt is the smallest amount that makes you feel as your own health goals determine. Sounds simple, doesn't it?
The problem lies in the fact that this amount varies considerably from woman to woman, and there are no hard and fast rules. Why? Among other things, remember what we said about endogenous production and xenoestrogens? It's impossible to know how much any given individual is obtaining from these sources, but they are a functional part of the overall quantity of hormones she has circulating in her body at any one moment. Of two surgically-menopaused women standing side by side, the one who has considerable belly fat, eats lots of tofu or red meat, and lives next to a toxic chemical waste site is probably going to need a lower additional dose of hormones than the other, who is skinny, eats fish caught on the open ocean and lives on a pristine island.
Aside from that sort of general consideration, it is also a rule of thumb that younger women require higher doses of HRT than older women. Our bodies do adjust to lower hormone levels as we age, and since many cancer risks relate to lifetime exposure, it's a good thing to mimic that natural trend.
Given that, a woman of 20 should begin by looking at hormone doses that are higher than those appropriate for a woman of 50. Although most commercial brands of hormones come in a range of doses, there is a roughly equivalent "usual starting dose" that many doctors begin with as a ballpark guess. Don't feel you need to stay there, though, if that dose doesn't suit you.
Additionally, all of us on HRT need to rethink our doses every few years or so to make sure we're not taking more than we need.
Other important considerations that go into dose determination are health and lifestyle factors. For example, a woman who has a clotting problem or a history of some types of cancer may take a suboptimal, risk-minimizing dose to derive some protection against things like osteoporosis and cardiovascular disease while relying on supplementary measures to deal with other symptoms resulting from the low dose. Doses as low as 25% of the "usual starting dose" of many commercial hormones have been demonstrated effective in osteoporosis prevention, although they may not be enough to deal with vaginal atrophy, mood or libido.
Similarly, women who drink alcohol regularly may require lower doses of estrogen, since alcohol causes a temporary boost (of about 300% and lasting about 4-5 hours, except that women who drink regularly have generally elevated estrogen levels) to circulating estrogen levels that may drive someone who is otherwise at a good level into symptoms of excess estrogen.
Smoking, on the other hand, has the reverse effect on estrogen levels. A woman who smokes will need a higher dose, relatively speaking, than the same woman would if she did not. Smoking also significantly counteracts the protective effects of estrogen on the bones and cardiovascular system, and may raise the clotting risks of taking estrogens (although that pertains most to oral hrts).
There are also a number of drugs and nutritional supplements that interfere with the metabolism of hormones (and vice versa), such that you may need to adjust your dose to take them into account. Don't obsess about this, though: this is only something to take into account when starting or stopping these other factors throws your hormone dose out of balance. When you achieve a steady state of balance, it doesn't matter a great deal what the individual components are, so long as they are all taken consistently.
In practical terms, since diet and stress also factor in, it's impossible to maintain a truly steady state and all we can do is come as close as we can. In this respect, a woman in surgical menopause demonstrates the loss of resilience that even post-menopausal ovaries give her naturally-menopaused sisters.
By the way: don't be alarmed at the fact that one form of estrogen may have a "usual starting dose" of 1 mg while another brand may "start" at 0.625 mg. Each different chemical variation of a hormone will take a different dose amount for the same effective quantity of hormone.
Additionally, the route of hormone administration will affect the quantity you need (more about that in the discussion of HRT routes), even if the hormone is the exact same brand, because doses taken by different routes are metabolized differently. For example, if you were taking 0.625 mg of Premarin and your doctor switches you to the Estraderm patch, a roughly equivalent dose would be the 0.05 mg patch. Because of the route and hormone chemical structure difference, however, the actual effects of each on your system may be very different. There is no magic conversion table that tells you [this much of HRT #1] = [this much of HRT #2].
If it's starting to sound like one big guessing game, all we can say is: you're catching on. For women in surgical menopause, HRT is our own personal science experiment.
