Oseltamivir usually takes 1~3 days to have an effect, and the specific effect time is related to the severity of the disease and the timing of taking the drug, etc. Oseltamivir is a drug used to treat influenza. Oseltamivir is a kind of medication used for the treatment of influenza, most patients can return to normal temperature on the second day after taking the medication; a small number of patients need 2~3 days after taking the medication to see the effect, so there are some individual differences in the specific effect time. In order to promote the therapeutic effect of Oseltamivir, it is recommended that patients need to take the drug within 48 hours of contracting influenza, once more than 48 hours, it may lead to a decrease in the efficacy of Oseltamivir. Common adverse reactions to Oseltamivir include nausea, vomiting, runny nose, indigestion, and upper respiratory tract infections, etc. Oseltamivir is contraindicated in people who are allergic to Oseltamivir. Oseltamivir carries some risks and patients need to be supervised by a specialist.