Speaker: Jonathan Treasure. Principles of interaction are presented by one of the US experts in the field. Some interactions can be negative, for instance if an herb with anticoagulant action adds to the anticoagulant activity of warfarin or another anticoagulant drug, bleeding can theoretically occur. Some interactions can be positive, for instance if an herb can help reduce the amount of chemotherapy drug required, then toxic side effects can be reduced. Examples of potentially positive and negative interactions are presented. This discussion is continued in recording 04OH12: Clinical Examples of Herb Drug Interactions.