An important thing to remember if you take echinacea as an herbal supplement is that it won't typically prevent colds.
From myDNA.com:
The herbal supplement echinacea doesn't prevent colds.
That's the word from Klaus Linde, M.D., of the Center for Complementary Medicine Research at the Technical University of Munich in Germany. His latest study states that while the herbal supplement may shorten the duration and severity of cold symptoms, it does not prevent the common cold.