When adverse event reports (AERs) from herbal products are rigorously investigated, it is invariably found that the AER was not due to the intended herb, but rather due to the presence of an unintended or undeclared substance – most commonly a toxic botanical.7 The occurrence of toxic plants may be classified as substitutions, contamination or adulteration.

Contamination with other botanicals
The term contamination is generally used to describe the accidental inclusion of undeclared substances. There have been numerous cases of contamination with toxic botanicals of which the following are just a few examples:

• Rauwolfia serpentina and Mandrogora officinarium (toxic alkaloids) in Ginseng.8
• Seeds of Poison hemlock in anise seed
• Burdock root contaminated with Atropa belladonna.9 10
• Two Canadians poisoned by Comfrey tea contaminated with Atropa belladonna.11
• Belladonna has also been reported as a contaminant of Mallow, Nettles and Mate.12
• Plantain contaminated with Digitalis lanata (Foxglove), disseminated to over 150 companies over two years before ADRs prompted a FDA investigation.13

Some toxic botanical contaminants that are reported to be commonly found14 in industry
include: Atropa belladonna, Conium maculatum, Digitalis lanata, Illicium anisatum,
Symphytum x uplandicum.

Unfortunately, the scientific literature is also fraught with reports based upon misidentified or unidentified “herbal” products. The most common mistake made by health professionals and scientists new to the field of phytomedicine research is the failure to adequately identify and characterize the herbal material being used. For example, much of the Echinacea angustifolia research published prior to 1989 must now be considered suspect for two reasons. Chemotaxonomic research provided irrefutable evidence that at least some of the “angustifolia” material under study must have been a common substitute for Echinacea, Parthenium integrifolium.15 Secondly, taxonomic studies revealed that most of the genuine Echinacea material supplied was in fact E. pallida not E. angustifolia.16 In North America, investigations have revealed there is wide spread contamination of commercial E. angustifolia crops with non-medicinal species.

Undeserved reputations for toxicity have dogged a number of herbs because the correct identity and plant part were not indicated or properly established in the original report. Unfortunately, authors continue to cite these erroneous reports and so perpetuate the misinformation. Some of these cases are summarized below.17