A purple coneflower may sound more like a garden delight than something that you would use for medicinal purposes, but in 2005 it was the second highest selling herbal supplement in the U.S.  Most people are more familiar with the colourful plant's commonly used name - Echinacea.
There are estimates that the first uses of Echinacea occurred as many as 400 years ago when Native Americans used the herb to heal wounds and infections, such as boils. The herbal health practices of the plains Indians caught on and spread as far as Europe.
There was a sharp decline in the use of Echinacea during the mid 1940s when breakthroughs in antibiotics flourished.  Then, an explosion of interest in herbal products in the U.S. catapulted Echinacea into the limelight once again.
Today, Echinacea accounts for more than $21 million of the nearly $250 million of herbal supplements sold in the U.S. 
Of the nine species of Echinacea, only three are known to offer substantial health benefits: Echinacea pallida, Echinacea purpurpea, and Echinacea angustifolia. The parts of the plant that are above its roots yield the potent anti-infection properties and vary in strength in each species of Echinacea.
The preparations of the herbal supplement are oral in nature and include teas, capsules, and extracts. The preparations may contain a single species of Echinacea are a combination of the species.  This is one aspect of the supplement that makes evaluating its effectiveness difficult. Nevertheless, numerous studies are performed on Echinacea every year.
Today's common uses of Echinacea are not limited to wound treatment. Studies of the herb reveal that it might work as an effective immune system stimulant. Ear infections, athlete's foot, urinary tract infections, and hay fever are just a sample of the conditions that people treat with Echinacea. 
The common cold, which does not have a cure, is the one condition that people seek more often to treat with Echinacea. The medical profession spends a significant amount of research hours testing what the general public considers evident. It seems that a winter month does not go by without breaking news of the results of a new study testing the effectiveness of Echinacea in treating the common cold. Unfortunately, many of these studies are inconclusive.
Back in June of 2007, however, some promising news emerged about Echinacea and the common cold. A study conducted by the University of Connecticut revealed that Echinacea might offer more benefit than vitamin C in treating the common cold.
In fact, the study revealed that Echinacea had both treatment and prevention benefits. What makes this report so promising? It was the first study that involved a small study group, low doses of the herbal supplement, and the use of the species of Echinacea used less frequently by the public.  The fact that a large number of the participants experienced relief despite the low level controls is at the very least a positive indication of what Echinacea has to offer suffers of the common cold.
While the University of Connecticut study is promising and significant to better understanding the effects of Echinacea for treating and preventing the common cold, additional study is necessary to narrow the results.
The varying results of studies of Echinacea are generally attributed to the types of preparations used in the studies. Echinacea is available in a variety of preparations and strengths and there is a difference in effectiveness between the species of Echinacea.  There is also a difference in the preparation of Echinacea. Some manufacturers use additives that can have an effect on the herb's effectiveness.
The most documented evidence of the side effects associated with using Echinacea originate from the Australian Adverse Drug Reactions Advisory Committee (ADRAC), which is revered as providing the most reliable reporting system of adverse reactions of drugs in the world.
The most common side effects reported by the ADRAC include skin reactions, respiratory infections, and stomach problems. [5-6]
Studies of Echinacea echo the side effects reported by ADRAC. The side effects that are reported most often when using Echinacea are related to the gastrointestinal tract. A recent study of 15 individuals who used 1000 mg of purpurea Echinacea for a period of 10 days concluded that the herbal supplement changed the bacterial composition of the gastrointestinal tract, which could possibly lead to a higher risk of colon cancer and inflammatory bowel disease. 
The second most common side effect of Echinacea is a variety of allergic reactions. According to the current studies, there is a higher incident of allergic reactions in people who had an existing allergy of daisy plants. 
Echinacea is readily available with other herbal supplements. While current studies do not reveal any drug interactions for Echinacea, it is best to discuss your plans of using the supplement with your doctor.