Tamiflu (oseltamivir) is a prescription drug used to treat and help prevent influenza (the flu). Tamiflu can cause side effects that range from mild to serious. Examples include nausea, vomiting, and headache.

Specifically, Tamiflu is used in adults and children to help:

  • treat the flu in people ages 2 weeks and older who have had flu symptoms for 48 hours or less
  • prevent the flu in people ages 1 year and older

Tamiflu comes as an oral capsule and an oral liquid suspension (a powder mixed with liquid by your pharmacist). Tamiflu contains the active ingredient oseltamivir.

Keep reading to learn about common, mild, and serious side effects Tamiflu can cause. For a general overview of the drug, including details about its uses, see this article.

Some people may experience mild to serious side effects during Tamiflu treatment. Examples of the drug’s commonly reported side effects include:

  • headache
  • nausea*
  • vomiting

* To learn more about this side effect, see the “Side effects explained” section.

Mild side effects have been reported with Tamiflu. These include:

  • headache
  • nausea*
  • vomiting
  • general body pain

In most cases, these side effects should be temporary. And some may be easily managed. But if you have symptoms that are ongoing or bothersome, talk with your doctor or pharmacist. And do not stop taking Tamiflu unless your doctor recommends it.

Tamiflu may cause mild side effects other than those listed above. See the drug’s prescribing information for details.

* To learn more about this side effect, see the “Side effects explained” section.

Serious side effects have been reported with Tamiflu, including mental health changes. To learn more, see the “Side effects explained” section below.

If you develop serious side effects while taking Tamiflu, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with Tamiflu, visit MedWatch.

Allergic reaction

For some people, Tamiflu can cause an allergic reaction. This wasn’t a side effect seen in Tamiflu’s studies, but it has been reported since the drug came on the market.

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a treatment to manage your symptoms and can determine whether you should keep taking Tamiflu.

If you have symptoms of a severe allergic reaction, such as swelling or difficulty breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms you’ve had a serious allergic reaction to Tamiflu, they may have you switch to a different treatment.

Get answers to some frequently asked questions about Tamiflu’s side effects.

Is Tamiflu an antibiotic?

No, Tamiflu isn’t an antibiotic. Tamiflu is used to treat influenza, which is a virus, so it’s considered an antiviral medication.

Is Tamiflu safe for older adults?

Yes. The safety and effectiveness of Tamiflu were no different in adults ages 65 years and older than in younger people in the drug’s studies. Talk with your doctor if you have concerns about taking Tamiflu due to your age.

How do Tamiflu side effects in children compare with those in adults?

Side effects were similar in children and adults in Tamiflu studies.

In children ages 1 to 12 years, vomiting was the only side effect commonly reported. Tamiflu was taken for both influenza treatment and prevention in these children.

Vomiting was also a common side effect reported by adults taking Tamiflu for the treatment and prevention of influenza.

In children ages 2 weeks to 1 year, vomiting, diarrhea, and diaper rash were commonly reported side effects. These children were taking Tamiflu for influenza treatment.

Talk with your doctor if you have additional questions about side effects of Tamiflu in children.

Below is important information you should consider before taking Tamiflu.

Warnings

Tamiflu doesn’t have any contraindications or boxed warnings. A contraindication is a factor or condition that could prevent your doctor from prescribing a drug due to the risk of harm. A boxed warning is the most serious warning from the FDA. It alerts doctors and patients about drug effects that may be dangerous.

Other warnings

Tamiflu can sometimes cause harmful effects in people with certain conditions. This is known as a drug-condition interaction. Other factors may also affect whether Tamiflu is a good treatment option for you. Talk with your doctor about your health history before taking this drug. Be sure to tell them if any of the following factors apply to you:

Learn more about some of the side effects Tamiflu may cause.

Behavioral changes

Mental health changes are serious side effects that can occur from taking Tamiflu. Mental health changes weren’t seen in the drug’s studies but have been reported since Tamiflu was approved for use. These changes—which often started suddenly and resolved quickly—were more commonly reported in children. It’s unclear how often this has happened or if Tamiflu was the cause, but such mental health changes can lead to injury and death.

Mental health changes may cause symptoms such as:

What might help

Talk with your doctor right away if you or your child develop any of the above symptoms while taking Tamiflu.

Nausea

Nausea was a common side effect reported in studies of Tamiflu. Nausea may cause symptoms such as stomach discomfort and a desire to vomit.

What might help

Taking Tamiflu with food may reduce your risk of nausea and upset stomach. If your symptoms are ongoing or bothersome, talk with your doctor. They can provide recommendations to help manage this side effect.

Keeping track of side effects

During your Tamiflu treatment, consider taking notes on any side effects you’re having. You can then share this information with your doctor. This is especially helpful when you first start taking a new drug or using a combination of treatments.

Your side effect notes can include things such as:

  • what dose of the drug you were taking when you had the side effect
  • how soon you had the side effect after starting that dose
  • what your symptoms were
  • how your symptoms affected your daily activities
  • what other medications you were taking
  • any other information you feel is important

Sharing notes with your doctor will help them learn more about how Tamiflu affects you. They can then use this information to adjust your treatment plan if needed.

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.