Clinically based evidence of drug-herb interactions: a systematic review

Importance of the field: Healthcare practitioners are deeply concerned about drug herb interactions and how concurrent administration may affect both the safety and effectiveness of prescribed drugs. Interactions between botanical medicines and synthetic drugs can be clinically relevant and it is important to understand what kinds of interactions are possible. Better knowledge in this area will help avoid negative interactions and may also help enable synergistic interactions. Areas covered in this review: Includes articles related to the investigation of Western botanicals or whole herbal extracts in human subjects, investigating either the impact on Cytochrome P450 isoenzymes or an assessment of specific drug herb interactions within a clinical trial. Searches were conducted in both Pubmed and EMBASE from inception to March 2009. What the reader will gain: Knowledge regarding specific interactions to consider in clinical practice. The reader will also gain an appreciation of the complexities associated with the area of drug herb interactions. Summary tables of relevant drug herb interactions are presented both for the individual herbs included and at the level of the CYP450 enzymes. Take home message: Knowledge of drug herb interactions is limited and much more research needs to be done to further document clinically relevant interactions. Even though preclinical data are often poorly generalizable to the human situation, caution must be taken in the absence of clinical evidence especially where drugs with narrow therapeutic windows are concerned.