Final answer:
Echinacea is a popular herb used in the U.S. to potentially reduce cold and flu symptoms, but scientific evidence of its effectiveness is insufficient. Zinc gluconate, however, has been found in some studies to be effective in reducing the duration and severity of colds when administered quickly after symptom onset.
Step-by-step explanation:
In the U.S., the herb Echinacea is often touted for its potential to reduce the severity and duration of cold and flu-like illnesses. However, despite its popularity for this use, evidence regarding its effectiveness is mixed. According to a 2014 review, there is insufficient evidence for Echinacea's efficacy in preventing or treating the common cold. On the other hand, the use of another substance, zinc, specifically in the form of zinc gluconate, is supported by some clinical trials. These studies suggest that when taken within 24 hours of the first symptoms, zinc can reduce the duration and severity of the common cold in healthy individuals. Caution is advised with zinc nasal products, as they may be associated with a risk of loss of smell.