Learn about common and serious Oseltamivir (Tamiflu) side effects, what's normal, and when you should contact your doctor right away.
Oseltamivir (brand name Tamiflu) is one of the most widely prescribed antiviral medications for the flu. Like all medications, it can cause side effects — but most of them are mild and go away on their own.
This guide covers the common side effects you might experience, the rare but serious ones to watch for, and clear guidance on when to contact your doctor.
The most frequently reported side effects of Oseltamivir are related to the stomach and digestive system. These are usually mild and tend to improve within a day or two of starting treatment.
Common side effects include:
It can be tricky to tell which symptoms are from the flu itself and which are from the medication, since nausea, headache, and stomach problems are common with both.
Serious side effects from Oseltamivir are rare, but they do occur. It's important to know what to watch for so you can get help quickly if needed.
There have been reports of unusual behavioral changes in people taking Oseltamivir, particularly in children and teenagers. These events are rare, but they can be alarming.
Watch for:
What to do: If you or your child experiences any of these symptoms, stop taking Oseltamivir and contact your doctor or go to the emergency room immediately. These events are more commonly reported in pediatric patients, but adults should be aware too.
It's worth noting that the flu itself can also cause neuropsychiatric symptoms, especially with high fever. Researchers are still working to determine how often these events are caused by the medication versus the illness.
Although very rare, some people have had serious allergic reactions to Oseltamivir.
Seek immediate medical attention if you experience:
In extremely rare cases, Stevens-Johnson syndrome (a severe skin reaction) has been reported. If you develop a widespread rash with blistering and peeling skin, seek emergency care immediately.
Rare cases of hepatitis and elevated liver enzymes have been reported with Oseltamivir use.
Contact your doctor if you notice:
Oseltamivir is FDA-approved for treating flu in children as young as 2 weeks old. The side effect profile in children is similar to adults, with some differences:
If your child is taking Oseltamivir, monitor them closely for any unusual behavior, especially during the first few days of treatment. If your child vomits within an hour of taking a dose, contact your doctor about whether to give another dose.
Oseltamivir is a Category C medication in pregnancy. The CDC recommends that pregnant women with the flu be treated with Oseltamivir because the benefits of treating influenza during pregnancy generally outweigh the potential risks. If you're pregnant and have concerns about side effects, talk to your OB-GYN.
No dose adjustment is needed for older adults with normal kidney function. However, older adults may be more susceptible to dehydration from nausea and vomiting, so staying hydrated is especially important.
If you have kidney problems, your doctor may prescribe a lower dose of Oseltamivir. This is because the medication is cleared through the kidneys, and reduced kidney function can lead to higher drug levels in the body. Make sure your doctor knows about any kidney issues before starting treatment.
If side effects are a concern, it may help to know how Oseltamivir compares to other flu medications:
Talk to your provider about which option is best for you. You can also learn more about how Oseltamivir works to understand why these side effects occur.
Yes, though it's uncommon. The only absolute contraindication for Oseltamivir is a known hypersensitivity to the medication or any of its ingredients. If you've had a reaction to Oseltamivir or Tamiflu in the past, tell your doctor before being prescribed it again.
Oseltamivir has relatively few drug interactions, but some are worth knowing about. For example, if you recently received the live nasal flu vaccine (FluMist), Oseltamivir may reduce its effectiveness. If you take Probenecid, it could increase Oseltamivir levels in your body. For a complete overview, read our guide on Oseltamivir drug interactions.
For mild side effects like nausea or headache, you should generally continue taking Oseltamivir and complete your full course of treatment. Taking it with food can help with stomach-related side effects.
However, you should stop taking Oseltamivir and contact your doctor immediately if you experience:
Never stop a medication without consulting your healthcare provider if you can avoid it.
You focus on staying healthy. We'll handle the rest.
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