Three closely related species of flowers— Echinacea (E.) purpurea, E. angustifolia, and E. pallida— are widely used in Europe and the U.S. to treat colds and flus. Double-blind, placebo-controlled studies enrolling a total of more than 800 people have found that various forms and species of echinacea can reduce cold symptoms, and help you get over a cold faster.

However, a recent study failed to find echinacea effective. While at first this might appear to discredit previous findings, a close look indicates that it has another meaning altogether.

The Barrett Study

In the December 17, 2002 edition of the Annals of Internal Medicine , BP Barrett and colleagues published the results of a double-blind, placebo-controlled study done to evaluate the effectiveness of a new echinacea product. In this well-designed and well-reported trial, 148 college students coming down with a cold were randomly assigned to receive placebo (333 mg alfalfa) or a dry herb echinacea product (25% above ground E. purpurea , 25% E. purpurea root, and 50% E. angustifolia root, along with small amounts of thyme and peppermint to disguise the taste.)

On the first day of treatment, each participant took six doses; on subsequent days, this was reduced to three doses per day. Treatment was continued until symptoms subsided, or for a maximum of 10 days.

The results failed to show any benefit. People taking echinacea did not recover any faster nor experience milder symptoms than those taking placebo.

What the Findings Mean

However, the researchers note that this trial has several important weaknesses. Foremost among them is the echinacea product used. Most studies of echinacea have used standardized extracts of the herb rather than dry herb (as used in this study). In addition, the products tested in the positive trials have generally consisted of the above-ground portion of E. purpurea . There is already some evidence that E. purpurea is ineffective, and E. angustifolia has scarcely been studied at all.

Thus, this study may only indicate that a particular echinacea product does not aid in the treatment of colds, rather than that all echinacea products are useless for this purpose.

In addition, this study only enrolled college students, unlike other studies that enrolled people of all ages. It is at least possible that echinacea has less to offer young people, whose immunity is presumably quite strong, than older people who may have weaker immune systems; there is no meaningful evidence for such a distinction, however.

Finally, the choice of placebo for this study has been questioned. Researchers used alfalfa, an herb with many biologically active constituents. Although alfalfa has no reputation as a treatment for colds, there is a theoretical possibility that it could offer some benefit in this regard. Any such effect would have tended to hide potential benefits caused by echinacea.

What Does This Mean for You?

This study highlights a very important way in which herbs are different from drugs. When you purchase a drug, you generally know exactly what you are getting. Drugs are single chemicals that can be measured and quantified down to their molecular structure. Thus a tablet of extra-strength Tylenol contains 500 mg of acetaminophen, no matter where or when you buy it. The same is true of a vitamin C tablet, provided that it is correctly labeled.

But herbs are living organisms comprised of thousands of ingredients, and between one plant and another the proportions of all these ingredients may be dramatically different. Numerous influences can affect the nature of a given crop. Whether it was grown at the top or bottom of a hill, what the weather was like, what time of year it was picked, what other plants lived nearby, and what kind of soil predominated are only a few of the factors that can affect the chemical make-up of an herb.

This presents a real problem with using herbal therapies. Since so much variation is possible, it’s difficult to know whether one brand of herb is equivalent in effectiveness to another. For this reason, it may be best to use the same brands that have been tested and found effective in double-blind studies. You can often find this information by reading the label closely. Another option is to use herbal products that have been found to be very similar in their constituents to tested products (see Resources).