Based on one study, herbal supplements are not very safe for those with certain allergies, especially to nuts. Most herbal products tested were of poor quality and contained product substitutions, contamination and use of fillers, therefore diluting the effectiveness of the herbal formula.
44 herbal products were tested blindly tested representing 12 different companies. Over half or 59% of the products tested contained DNA barcodes from plant species not listed on the labels. Less than half (48%) of the products were authenticated. However, one-third of these were contaminated or had fillers not listed on the label. Product substitution occurred in 30 of the 44 of the products tested and only 2 of the 12 companies had products without any substitution, contamination or fillers (such as rice, soybeans, and wheat not listed on the label). Some of the contaminants found could pose serious health risks to consumers. For instance, one product had black walnut in it but was not listed on the label. Those with serious nut allergies would be at risk.
For quality herbal and vitamin supplement products, only buy with the GMP (Good Manufacturing Practice) seal of approval on their label. GMP guidelines require compliance through an independent third party audit for product approval. NOW Food and Rainbow Light supplements are two of several companies that have the GMP seal of approval. Check labels carefully.
If you have serious food allergies to soy, gluten, nuts, etc., it is always best to call the manufacturer for a complete list of ingredients before using any product.