It is intended to provide an activity enhancer and/or a side effect-lessening agent for an IFN agent containing glycine as the active ingredient which is an excellent activity enhancer and/or a side effect-lessening agent for an IFN agent being capable of enhancing the activity of the IFN agent and/or lessening the side effect thereof in a therapy with the use of the IFN agent. It is also intended to provide an antiviral agent, a remedy for viral hepatitis, an antitumor agent, a remedy for autoimmune diseases, a food composition and so on containing the activity enhancer and/or side effect-lessening agent for an IFN agent.
