while there are many alternative treatments used for the common cold, there is not enough scientific evidence to support the use of most treatments. as of 2010, there is not enough evidence to recommend for or against either honey or nasal irrigation. zinc supplements may reduce the severity and duration of symptoms when taken within 24 hours of their onset. the effect of vitamin c on the common cold, while extensively researched, is disappointing. evidence about the usefulness of echinacea is inconsistent. different types of echinacea supplements may vary in their effectiveness.