A team from ConsumerLab.com found that out of eleven products that contained echinacea five failed to pass independent testing. Lower than claimed amounts of key compounds such as echinacosides and phenols were the most common problem. One product contained a higher than acceptable amount of lead.
Echinacea was the top-selling single herb in 2002, with sales of $187.9 million, representing 10 per cent of the dietary supplement market in the US. The herb is sold in different forms - capsules, liquid - and only some products label the concentration of echinacea present - normally an indication of the quality of echinacea used.
The researchers evaluated echinacea products to determine whether they contained the claimed and expected amount and type of echinacea. They also screened for microbial and lead contamination. They report their findings on their website.
Of the 11 samples tested, one contained excessive lead contamination with 2.5 micrograms of lead per daily serving exceeding the California state limit. Three products were low in phenols - plant chemicals used to judge the quality of echinacea. It is believed that higher phenol levels relate to higher potency.
One product's label claimed its amounts of phenols and echinacea were based on a method of analysis that was not an industry standard. Using a more specific and accepted form of testing lower concentrations of these ingredients were found.
Tod Cooperman, President of Consumerlab.com said: "If you are not getting the expected effect with echinacea, it may be the brand."
"Products may fall short for many reasons: The wrong plant species or plant part may be used; levels of important plant chemicals may be low if the herb is not properly grown, harvested, processed, shipped and stored; and lead levels may be high due to contaminated soil."
Despite the huge variation of different blends and concentrations available on the market, very few have been tested. There have been estimates of around 200 different forms, from teas to capsules, sold nationwide.
The Journal of the American Medical Association reported in December 2003 on a syrup made with the herb, which reduced the number of respiratory tract infections in children but did not reduce the severity or duration of the infection.
Researchers at the University of Wisconsin, US, went one step further and claimed echinacea, when used to treat the common cold, had no effect when tested on a small group of students with colds.