The aim of this randomized, double-blind, placebo controlled study was to investigate the efficacy and safety of different doses and preparations of Echinacea purpurea in the treatment of common cold. 246 of 559 recruited healthy, adult volunteers caught a common cold and took 3 times daily 2 tablets of either Echinaforce (Echinacea purpurea-preparation from 95% herba and 5% radix), Echinacea purpurea concentrate (same preparation at 7 times higher concentration), special Echinacea purpurea radix preparation (totally different from that of Echinaforce) or placebo until they felt healthy again but not longer than 7 days. The primary endpoint was the relative reduction of the complaint index defined by 12 symptoms during common cold according to the doctor's record. Echinaforce and its concentrated preparation were significantly more effective than the special Echinacea extract or placebo. All treatments were well tolerated. Among the Echinacea groups the frequency of adverse events was not significantly higher than in the placebo group. Therefore, Echinacea concentrate as well as Echinaforce represent a low-risk and effective alternative to the standard symptomatic medicines in the acute treatment of common cold.