A new study out of the University of California San Francisco casts doubt on echinacea's ability to prevent colds.

This latest study, published in the Annals of Allergy, Asthma and Immunology, adds to doubts about echinacea's ability to prevent colds.

Researchers at the University of California San Francisco followed 58 volunteers for eight weeks and found no definitive evidence that echinacea prevented nasal congestion, sore throats and other cold symptoms.

The study was published in the Annals of Allergy, Asthma and Immunology.

Study participants took either three echinacea capsules or three placebo capsules containing parsley twice daily.

While the echinacea group reported fewer sick days than the placebo group, nine versus 14, researchers chalked the difference up to chance.

"Although echinacea is touted as an immune stimulant and sold in almost all health food stores, this study is one of many with equivocal findings that really do not support the use of echinacea to prevent the common cold," lead researcher Dr. Joelle O'Neil told Reuters Health.

Click here to see the study.