Principle of Bach Flower Essences
They could be classified as herbal remedies because of their origins. However, this is not completely true. Their action is not chemical or pharmacological. They work on the mental level purely through their "vibrations". Vibrational remedies don't contain a substance that works. They contain the "signature" or vibration of a particular substance. That vibration resonates with the vibration of human cells.
Chemical tests would only reveal water and brandy (as preservative), the flower essence and its action cannot be detected in this way.