Many of our conventional drugs come from the purified extracts of herbal preparations. However, herbalists claim that one of the great strengths of using the unrefined whole plant is that the active ingredient is given along with a number of other naturally occurring plant chemicals and this, in itself, makes the action of the active ingredient far safer and so diminishes the chance of unpleasant side effects. Such views represent an attractive, but as yet unproven, hypothesis. Herbalists will tend to use many herbs in combination, the combinations are largely based on clinical experience rather than rigorous science. It seems that in conventional medicine we are trying to decrease the number of drugs we give to people, whereas in herbal medicine sometimes the opposite occurs. As with many other forms of complementary medicine, the prescription of a specific herb or mixture of herbs is not based on a conventional medical diagnosis but rather on the traditional diagnostic system that underpins the herbal prescription. For instance, a herb may be prescribed the strengthen the kidney or liver or to dispel heat.