The simple purple coneflower has become a popular natural cure-all for colds and flu symptoms. Preparations are derived from three of the nine species. A liquid form of Echinacea purpura is the most widely used form in this country.1 The genus name is derived from the Greek word echino, meaning “hedgehog,” a reference to the flower’s spiny central disk, which is surrounded in a cone shape by purplish-pink petals. Standing two to three feet tall, all parts of the plant are used for medicinal purposes.2

History

Echinacea has long been used by Native Americans to treat a variety of conditions, from colds and cramps to sepsis, measles, and even cancer. Individuals would suck on the plant’s root, apply poultices to wounds, and drink teas made with the herb. In the late 19th century, a physician patented “Meyer’s Blood Purifier,” which contained echinacea, hops, and wormwood.

Early literature abounds with references to echinacea’s usefulness. The plant was brought to the attention of the medical community in 1887 after John King, MD, in King’s American Dispensatory, mentioned echinacea as a treatment for bee stings, nasal congestion, and infant cholera. In 1917, pharmacist John Uri Lloyd, MD, wrote a detailed historical account of the herb in A Treatise on Echinacea.3 He predicted that “[echinacea] will be ardently sought and widely used.” In the 1919 book, Uses of Plants by the Indians of Missouri River Region, noted anthropologist Melvin R. Gilmore wrote that echinacea was “universally used as an antidote for snakebite and other venomous bites and stings and poisonous conditions.”3

Scientific data

Despite the fact that echinacea liquid extract is listed as the most widely used herbal product in the United States, firm clinical data are scarce.4 Sales of all forms of echinacea account for more than 10% of the U.S. supplement market,1 but, to date, two large trials have failed to show substantial benefit in shortening the course of colds or flu.2 In a recent trial, 399 healthy patients were randomized to either an echinacea extract or placebo and then exposed to the cold virus. No difference in infection rate was noted between the two groups.5 On the other hand, a recent meta-analysis of three trials showed that development of cold symptoms after exposure was decreased by 55% with the use of echinacea vs. placebo.1

There is an established lack of benefit in children aged 2-11,1 most likely due to immature immune systems. Like most herbal studies, the findings from echinacea trials are conflicting. Studies vary widely in their designs, often with very few subjects and without randomization or placebo controls. One of the largest studies in children (N = 407) found that echinacea failed to alleviate cold symptoms and even caused mild skin rashes.6 A review of 16 trials showed a statistical trend toward a positive effect, but because of the variation of product preparation and study design, no quantitative conclusion could be reached.4

Mechanism of action

The beneficial action of echinacea is thought to be an effect of one or more of the three classes of alkylamides, chicoric acids, and low-molecular-weight polysaccharides.7 Each compound exhibits immunostimulatory properties in vitro. Specifically, they stimulate phagocytes and increase respiratory cellular activity and mobility of leukocytes.7 Although all three compounds are active, each has a specific action. The caffeic acid/low-molecular-weight polysaccharides stimulate phagocytosis, while the alkylamides exert anesthetic and anti-inflammatory actions.7 Further studies suggest an increase in interferon levels and up-regulation of tumor necrosing factor, interleukin-1 and interferon-β2, although studies of echinacea’s use in HIV-infected patients show no effect.8

Dosage

The recommended dose depends on what form of the product is used. Echinacea is available in liquid form, tablets and capsules, and tea. Tinctures and juice extracts tend to be more concentrated. Typical doses of these hydroalcoholic extracts are 2-4 mL of 4%-5% echinocoside t.i.d.8 Capsules of powder-ground root and plant fiber are given in 325- to 650-mg dose ranges t.i.d.8 Dosing should not last longer than eight weeks, and, in most cases, daily use for 10-14 days is sufficient.7

Echinacea is also available in combination with other supplements, especially zinc and vitamin C. Depending on the type of preparation and brand, a three- to four-month supply will cost $8-$20.

Drug interactions and safety

Echinacea is a pollen-bearing plant and therefore possesses definite allergenic potential. Reactions occur most commonly in those who are allergic to other members of the daisy family, including ragweed, marigolds, and chrysanthemums. Challenge doses should be administered cautiously in patients with a history of atopy or asthma. Reported adverse effects are rare and include GI upset, nausea, rash, and anaphylaxis. Echinacea is not indicated for use in children. Women who are pregnant or lactating should also avoid it.

Drug interactions have been noted, specifically in inhibiting the cytochrome P-450 enzyme chain.8 Echinacea should not be given to transplant patients because its potential for metabolic interference may weaken the effect of immunosuppressants.8 In spite of echinacea’s potential for stimulating the immune system, it is not recommended for persons with an immunocompromising illness, such as HIV, collagen disease, or multiple sclerosis.8 Liver function should be monitored because transient elevations have been noted.7

Summary

Data substantiating the efficacy of echinacea as an immune-enhancing herb is scarce, at best. Though relatively safe, there is actually more evidence to show the plant’s lack of efficacy than the contrary. The best defense against cold and flu remains frequent hand-washing, adequate rest, hydration, and avoidance of exposure whenever possible.

References

1. Natural Standard Patient Monograph. Echinacea (E. angustifolia DC, E. pallida, E. purpurea). Available at mayoclinic.com/health/echinacea/NS_patient-echinacea. Accessed September 10, 2006.

2. National Center for Complementary and Alternative Medicine. Herbs at a glance: Echinacea. Available at nccam.nih.gov/health/echinacea. Accessed September 10, 2006.

3. Foster S. Echinacea. Available at www.herbalgram.org/default.asp?c=echinacea. Accessed September 10, 2006.

4. Kliger B. Echinacea. Am Fam Physician. 2003;67:77-80, 83.

5. Turner RB, Bauer R, Woelkart K, et al. An evaluation of Echinacea angustifolia in experimental rhinovirus infections. N Engl J Med. 2005;353:341-348.

6. Echinacea fails to treat or prevent colds in study. Available at www.msnbc.msn.com/id/8728355/. Accessed September 10, 2006.

7. Fetrow CW, Avila JR. Professional’s Handbook of Complementary & Alternative Medicines. Springhouse, Pa.: Springhouse Corporation; 1999:400.

8. Skidmore-Roth L. Mosby’s Handbook of Herbs & Natural Supplements. 3rd ed. St. Louis, Mo.: Elsevier Mosby; 2006:232.