Does Tamiflu work?

By Eileen Bailey | Updated on Aug. 4, 2023 Medically reviewed by Karen Berger, Pharm.D.

Just because flu season affects many people annually, doesn’t mean it is a virus to take lightly. It can have serious complications, especially for certain populations. If you’re in a high risk group, your healthcare provider might prescribe Tamiflu (oseltamivir phosphate) at the first sign of flu symptoms. Three physicians explain Tamiflu effectiveness, and how to know if you should take it.

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What exactly does Tamiflu do?

Tamiflu is an antiviral drug that blocks influenza A and B by attacking the virus and stopping it from multiplying, according to the Food and Drug Administration (FDA). Tamiflu does not work on other viruses or bacterial infections.

Preparation—read: getting an annual flu vaccine—is the best way to avoid catching this respiratory infection. Tamiflu is sometimes used to prevent flu for people exposed to the influenza virus, but it is not an effective substitute for immunization.

If you do get the flu, Tamiflu can reduce the intensity of symptoms and reduce the amount of time that you feel sick.

How effective is Tamiflu?

Tamiflu can reduce complications of the flu (such as pneumonia) by 44%, and the risk of hospitalization by 63% when taken in the first 48 hours after contracting the virus, according to the makers of Tamiflu. When used to prevent the flu in people exposed to the virus, it reduced the probability of becoming sick by up to 55%, says the National Center for Health Research.

“Tamiflu is not a cure for the flu,” explains Michael Carnathan, MD, a family physician in Bethlehem, Pennsylvania. “It won’t completely eliminate all of your symptoms, but it usually shortens the duration of the symptoms. It is most effective when started within the first 24 to 48 hours after the first symptom. Don’t be afraid to contact your doctor at the first sign of a fever and body aches.”

Does Tamiflu work after 48 hours?

Not sure if you have flu symptoms? You might wake up with a fever and aches and pains, or you might come home from work not feeling well. “Flu symptoms often appear suddenly and make you feel as if you were hit by a Mack truck,” says Genevieve Brauning, MD, a family medicine practitioner with Novant Health in Charlotte, North Carolina. And the first sign of symptoms is when you need to act. “Because there is only a short window of time to take Tamiflu so it is effective, it is best to contact your doctor immediately. After 48 hours, it might not be worthwhile to take Tamiflu.”

How quickly does Tamiflu work?

For the treatment of influenza, Tamiflu should be taken for five days after flu symptoms start. Adults and adolescents (13 years and older) may take 75 mg twice a day for five days. Flu symptoms typically last for five to seven days, but Tamiflu can reduce the duration and severity of flu symptoms.

How long are you contagious with the flu after taking Tamiflu?

It’s important to note that you’re still contagious after taking Tamiflu. Meaning, you can transmit the virus to others, so just because you start the antiviral medication doesn’t mean you can go out and about.

If you think you have the flu, you should always call your healthcare provider instead of waiting to see if you improve. It is better to be told you don’t have it than to hold off calling and suffer through a week or more of debilitating symptoms.

Is Tamiflu safe?

Tamiflu is very safe, and it’s effective for patients as young as 2 weeks old. However, you should always discuss the benefits and risks of taking Tamiflu with your healthcare provider.

Tamiflu can have side effects (usually occurring within the first two days), and for some people, these can be worse than having the flu, according to Dr. Brauning. The most common side effects of Tamiflu include:

Abdominal pain
Nausea
Vomiting
Headache

According to the FDA, children and adolescents with the flu are at an increased risk for serious side effects like seizures, confusion, and abnormal behavior. Even though the FDA has approved Tamiflu for young children, Dr. Brauning is always cautious when prescribing it for children because of the side effects. You should consult your child’s pediatrician before giving them Tamiflu.

Who should (and shouldn’t) take Tamiflu?

Tamiflu is best for patients who are at high risk of developing severe complications from the flu virus. This includes very young children, the elderly, immunocompromised patients, patients with diabetes, heart disease, asthma, and other chronic diseases, and nursing home residents.

Patients with mild to moderate liver impairment can safely take Tamiflu. Patients with severe liver disease should speak with their doctor as to whether or not it is safe to take Tamiflu. In patients with mild kidney issues or with end-stage renal disease and on dialysis, the dose of Tamiflu will likely be adjusted. But, Tamiflu is not recommended for people who have end-stage renal disease and are not on dialysis.

The Centers for Disease Control and Prevention (CDC) also recommends Relenza (zanamivir), Rapivab (peramivir), and Xofluza (baloxavir marboxil). If Tamiflu isn’t right for you, you might ask your healthcare provider about these other flu treatments in addition to over-the-counter medicine and supplements for alleviating symptoms and boosting your immune system.

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Is Tamiflu safe if you are pregnant?

“Women who are pregnant should seek medical help at the first sign of flu because they are at high risk of complications from the flu,” says Alyse Kelly-Jones, MD, a gynecologist with Novant Health in Charlotte, North Carolina. The flu is risky for expectant mothers and their babies. “It can be fatal during pregnancy, and it also increases the risk of preterm labor, which puts the baby at risk of health complications,” she says.

Because there are no well-controlled studies in pregnant women, Tamiflu will only be prescribed if your doctor feels that the benefits outweigh the potential risks to the fetus. However, at the first sign of symptoms, or if you are running a fever, you should contact your primary care provider immediately. Because many offices prefer not to have someone with the flu in the waiting room (where they can spread it to other people), you may receive treatment over the phone. If you are experiencing additional symptoms such as shortness of breath, chest pain, or dehydration, consider emergency treatment to see if inpatient care is required.

When to call your doctor

Symptoms of the flu include fever, chills, body aches, weakness, and may include a sore throat, headache, or cough. While the common cold comes on gradually, flu symptoms appear quickly. If you experience any of these symptoms or have been exposed to someone diagnosed with the flu, you should call your physician’s office to see if Tamiflu is right for you. Remember, the first 48 hours are crucial for the most effective flu treatment, so do not hesitate to make that call.