Arbidol is an antiviral and immunostimulatory agent developed in the Russian Research Chemical-Pharmaceutical Institute. It has been launched in the Russian Federation for the prophylaxis and treatment of influenza A and B. The mechanism of action of arbidol has not been completely clarified, but it appears that the compound inhibits influenza virus/cell fusion, as well as inducing interferon and activating macrophage phagocytic function. The antiviral effect may be related to activation of 2,5-oligoadenylate synthetase. Arbidol may also be beneficial for patients with secondary immunodeficiency, in those with recurrent herpes infection and in those with chronic bronchitis.