The difference between herbal medicine and pharmaceutical medicine is the difference between aspirin and the bark of a Willow tree.
Aspirin is acetysalicilic acid, a synthetic chemical modeled on compounds called salicates originally found in the bark of Willows that reduce fever, inflamation, and pain.
But aspirin can cause gastrointestinal bleeding -- Willow bark does not. (In fact, at the turn of the century, Maude Grieve wrote in A Modern Herbal that White Willow (S. alba) bark "has been used in dyspepsia connected with debility of the digestive organs." And the bark of both White Willow and Black Willow (S. nigra) can be useful in treating diarrhea.)
This is because though modern medicine considers sacicates the "active compound" in Willow bark, they are not the only medicinal compounds in Willow. And biochemists have not yet decoded the chemistry of Willow bark (or Yarrow blossom or Skunk Cabbage root or any of the many other botanical medicines that contain salicates) well enough to understand how the many chemicals in the plant work together to negate the negative side effects that saclicylic acids have when they are introduced into the body alone.
Unlike the bark of the White Willow, aspirin is useless in treating infestations of parasitic worms. Unlike the bark of the Black Willow, aspirin is ineffective as an aphrodisiac and has no history of being used to treat cancers or stimulate hair growth.
And even if pharmeceutical companies completely decoded the chemistry of Willow bark and succeded in creating a synthetic pharmaceutical that could do all of these things, that pill could never sing in the wind or provide shade on the banks of a river on a hot summer day or teach us about strengh, grace, and bending. Or inspire words like "wise and witch." All of this is as much a part of Willow's medicine as its ability to ease pain an relieve fevers.
The humility to know that our minds cannot surpass the brilliance of a living, changing planet, and the vision to understand that the medicine is in the whole and not in the parts is the fundamental difference between pharmaceutical medicine and herbal medicine.