Echinacea, a plant also known as purple coneflower, is sold as an over-the-counter remedy for the common cold or flu. “Taking echinacea might slightly reduce your chances of catching a cold,” according to the National Institutes of Health, but the plant hasn't been shown to shorten its length.
There are few studies about echinacea’s effects on the lungs or other parts of the body. While it has been widely used for centuries for various ailments, the NIH notes there isn’t enough evidence of other benefits beyond its possible effect on colds. In rare cases people have experienced shortness of breath as a side effect, and people with asthma and allergies are at increased risk of such an adverse reaction.
Given the plant’s known properties, a December 2020 paper by researchers focused on natural remedies says “further research is warranted” into its potential against COVID-19.