Provided is a prophylactic/therapeutic agent forinfluenza viral infection that is effective not onlybefore and at an early stage of infection with influenzavirus but also at an intermediate or late stage of theinfection and is highly safe for human bodies. Aprophylactic/therapeutic drug for influenza viralinfection comprising, as active ingredients,5-aminolevulinic acid (5-ALA), a derivative thereof or asalt of the 5-ALA or the derivative, and an iron compoundis prepared. This prophylactic/therapeutic agent can beused for ameliorating (preventing) depression in foodconsumption, water consumption and body weight, forameliorating (decreasing) increase in ketone body levelsin blood that may otherwise cause ketosis, forameliorating (preventing) depression in ATP levels inblood, or for ameliorating (increasing) a survival rateand depression in a body surface temperature.
