Using posters, newspaper advertisements, and e-mail messages, the researchers recruited students to call at the first sign of cold symptoms. Students could participate in the study if they were 18 years of age or older, had cold symptoms that began within the past 36 hours, and reported at least 2 of 15 listed symptoms. They could not participate if they were pregnant; had certain medical illnesses such as asthma; or were taking antibiotics, antihistamines, or decongestants. The researchers then assigned students to receive either a capsule form of echinacea or a placebo (four tablets six times per day for the first day, then three times per day until cold symptoms resolved or 10 days had passed). The echinacea capsules were made of whole unrefined plant material (a combination of roots from Echinacea angustifolia and herbs and roots from Echinacea purpurea). The placebo looked and tasted like the echinacea capsules but contained no active ingredients. On each day of the study, students completed a detailed questionnaire about the presence and severity of cold symptoms on that day. The researchers then compared the time until all cold symptoms had resolved and the severity of 15 separate cold symptoms (dry cough, sore throat, runny nose, etc.) on each day of the study.