"An Herbalist's Guide to Formulary" is not a book you can use by itself unless you have an extensive knowledge of herbs. The author provided only very brief information about the herbs, focusing mainly on how the human body works (digestive, cardiovascular, brain & nervous, immune, hormones, etc.) and her formulas. By which I mean, use 2 parts tonic (supportive, long-term usage herb) to 1 part tier 2 herb to 1 part tier 3 herb to 1 part tier 4 herb.
So she'd talk about the respiratory system, for instance, and then list some herbs (tier 1, tier 2, etc.) that would be helpful for various problems with the respiratory system. She'd even suggest specific formulas (2 parts yarrow, 1 part sage, 1 part....taken as tincture). However, she didn't suggest how much of the herb to use (or even say how much was safe). The closest she got to giving amounts was "a small amount." As in, use kelp only in "small amounts due to high sodium content." (And she didn't mention the high iodine content here, which is a greater concern.) She didn't suggest how often or long one might take the formula. She didn't explain how to mix the herbs or make pills, tinctures, etc. She assumed you already know all this abut herbs.
Also, I found enough basic errors that I stopped trusting her information. While she generally had good information, she'd say things like constipation is caused by too much fiber (but the opposite is true). She suggested eating yogurt when you have an ulcer, but the current medical advice is to avoid all dairy when you have an ulcer. In one spot, she said to avoid dairy for that condition, then a few sentences later she suggested eating yogurt. She also said some things that were confusing due to not fully explaining what she meant. So she said several times that you shouldn't take garlic long-term, only much later explaining that she was referring to raw garlic. I believe I was reading an advanced reader copy, so maybe the errors will be fixed in the final copy.
I received an ebook review copy of this book from the publisher through NetGalley.