Medicines (as in western medicine) are not built unless they are created in a chemistry laboratory.
Herbal medicines are extracted, usually from more than one plant species and various methods are used, dependent upon what the medicine is to be used for.
The methods are tincture (herbs are soaked in alcohol to extract the components), decoction (herbs are boiled for various amounts of time but usually at least 5 hours to extract the components),
for extraction of herb components the usual solvents are; water, mineral oil or olive oil, alcohol (vodka is normally the choice).
Essential oil (the herbs are distilled thus releasing the volatile oils which contain the components)
I prefer to use multiple herbs in a formula instead of just a few. It seems to have a greater effect this way, this is something I've also learned from other herbalists.
Here's a link to some formulas for specific areas of the body to help you get started. Herbal Formulas Go down to my post within the link and you'll find a couple of files with those formulas.
Lately I've not even bothered with making tinctures, I've simply been grinding up the herbs and putting them in capsules. I am liking it far more than a tincture, it seems to be more effective as well.
My Food Forest - Mile elevation. Zone 6a. Southern Idaho <--I moved in year two...unfinished...probably has cattle on it.