In a placebo‐controlled double‐blind study, the therapeutic effect of Kan Jang tablets made from Andrographis paniculata (Barm. F.) (Ness) dried extract was tested in patients with common colds. The patients were divided in two groups, in which group 1 (n = 33) received 1200 mg of Andrographis paniculata and group 2 (n = 28) a placebo (P). On day 3–4 after treatment the possible effect of Kan Jang tablets on selected symptoms and clinical signs of common cold was evaluated. A significant reduction in clinical symptoms at day 4 of administration of the Kan Jang tablets was observed. A better efficacy against the placebo is discussed. The differences in the total ‘sumscores’ of clinical and symptomatic findings indicate that the Kan Jang treated group did far better than the placebo group. We conclude that Kan Jang in a dose of 1200 mg daily has the capacity to significantly shorten the course/duration of the disease and therefore is indicated for an enhanced resistance to common colds.