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Herb–Drug and Food–Drug Interactions

Part X. Clinical Aspects of Drug Metabolism and Interactions

  1. Martin S. Lennard

Published Online: 31 JAN 2012

DOI: 10.1002/9780470921920.edm124

Encyclopedia of Drug Metabolism and Interactions

Encyclopedia of Drug Metabolism and Interactions

How to Cite

Lennard, M. S. 2012. Herb–Drug and Food–Drug Interactions. Encyclopedia of Drug Metabolism and Interactions. X:1–27.

Author Information

  1. The University of Sheffield, Academic Unit of Medical Education, Sheffield, UK

Publication History

  1. Published Online: 31 JAN 2012


Medication with plants and herbs has been practiced for thousands of years, and a substantial proportion of the world's population is thought to use herbal medicines. Herbal medicines are likely to be taken with prescribed drugs, leading to the risk of herb–drug interactions. Herbal consumption can not only diminish the therapeutic effect of drugs but also give rise to adverse reactions and toxicity. These clinical effects are caused by changes in (i) pharmacokinetics, particularly through inhibition or induction of the cytochrome P450 drug-metabolizing enzymes, and (ii) drug receptor sensitivity. There are many instances where food itself and its constituents have been shown to influence the pharmacokinetics of and response to drugs, sometimes causing substantially diminished therapeutic effects or adverse reactions. Much of the published evidence on herb–drug and food–drug interactions is based on case reports or on pharmacokinetic data alone, and these require substantiation by studies measuring the clinical effects of drugs.


  • drug interactions;
  • herb–drug interactions;
  • food–drug interactions;
  • St. John's wort;
  • grapefruit juice