Common Side Effects of Oseltamivir

Oseltamivir, also known as the brand Tamiflu marketed by pharma giant Roche, is one of the most commonly prescribed anti-viral drugs prescribed for this purpose. 

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Flu ‘season’ begins every year in October and lasts a few months during the winter. Depending on the year, bouts of the seasonal flu can affect people well into the spring. The flu is spread by droplet infection from individual to individual and is caused by a group of viruses that belong to the Influenza group. Both Influenza Type A and Type B can cause symptoms of the seasonal flu in humans. Symptoms of the flu can vary and usually include fever, body ache, cough, sore throat and muscle pain.

Many people experience mild versions of the flu and can get better with home treatment that includes rest, drinking fluids and taking over-the-counter medication like Tylenol to reduce their fever. To reduce chances of contracting the flu, a vaccination is available and is recommended by the Centers for Disease Control and Prevention (CDC) at the beginning of every flu season.

Getting the flu shot can reduce your chances of getting the seasonal flu. If you still get the flu after getting a flu shot, you will most likely experience a milder form of the flu. 

Some individuals are at higher risk of experiencing a severe form of the flu. These people usually belong to the following groups:

  • Over the age of 65
  • Children below 5 years
  • Pregnant women
  • Pre-existing conditions that affect the heart or respiratory system like asthma
  • Conditions that weaken the immune system 
  • Immunocompromised individuals like people with HIV 
  • Hospitalized patients

People in any of these groups may experience severe symptoms of the flu and can take longer to get better. For these individuals, treatment with anti-viral agents that can target the Influenza Type A and B viruses is recommended.

Oseltamivir, also known as the brand Tamiflu marketed by pharma giant Roche, is one of the most commonly prescribed anti-viral drugs prescribed for this purpose. 

What is Oseltamivir?

What is Oseltamivir phosphate? Oseltamivir is an anti-viral drug that belongs to the class of neuraminidase inhibitors. The Influenza viruses use an enzyme called neuraminidase to cleave a component named sialic acid on human cells in order to complete their reproductive cycle.

This is a crucial step for the virus to replicate itself inside human cells. What is Oseltamivir Used For? Oseltamivir, like other neuraminidase inhibitors, inhibits the activity of neuraminidase and prevents viral replication from happening within the body.

Oseltamivir has been FDA-approved to treat the seasonal flu since 1999, and it is currently the most commonly prescribed anti-viral drug for Influenza infection. 

When to take Oseltamivir

Oseltamivir is indicated for the treatment of the seasonal flu and to shorten the duration of illness due to Influenza infection. Importantly, it is not indicated for preventing complications that arise due to the flu. These complications can include pneumonia and other respiratory infections.

Oseltamivir works best when taken within the first 48 hours of developing symptoms. The earlier you take oseltamivir after experiencing symptoms, the more effective it is supposed to be. To prevent the seasonal flu, oseltamivir is prescribed before symptoms appear in high-risk individuals or individuals that have been exposed to the flu.

Oseltamivir does not work to treat the common cold or infections caused by other viruses or bacteria. 

A prescription is necessary to purchase oseltamivir. So, if you think that you may need to take this drug, you must be evaluated by your physician first. 


Typically, oseltamivir is taken twice a day for five days to treat the flu in adults. To prevent the flu, oseltamivir is prescribed once a day for ten days. This medication should be taken exactly as prescribed by your doctor. It is generally safe for children and babies above 2 weeks.

The side effects can vary in children compare to adults though. More details about this are included below. It is not clear whether this medication is safe to be taken by pregnant women. Pregnant women who contract the flu must discuss whether to take oseltamivir with their doctor. 

Most common side effects 

As with any drug, oseltamivir has its share of reported side effects. When taking a new drug, it is good to be aware of what the common side effects might be. If your doctor prescribes oseltamivir to treat the seasonal flu, they have judged that the benefits of taking the drug will most likely outweigh the risks due to side effects caused by the drug.

Oseltamivir is associated with a few common side effects and some rare ones. These side effects should be reported to your doctor if you experience any of them. 

Nausea and Vomiting

Nausea and vomiting are the most commonly reported side effects of taking oseltamivir. These side effects are usually mild and tolerable by people who take the medication. The typical course of taking oseltamivir is about five days to treat the flu.

Nausea and vomiting usually occur after a few days of taking the medication, so even if you experience these side effects they are likely to resolve soon when you finish your course. Taking the medication along with food can help to reduce nausea and vomiting caused by oseltamivir and associated abdominal pain that may occur with it. 

Behavioral and Psychological Problems

Some cases of psychiatric changes have been reported by people who take Tamiflu. These side effects are mostly observed in children taking the medication and are rarely reported by adults. These side effects include sudden mood or behavioral changes, hallucinations, seizures, dizziness and rarely even suicidal thoughts have been reported in children.

It is not clear whether these psychiatric symptoms are directly caused by the oseltamivir, but any signs of such changes in an individual taking the medication should be reported immediately. Since these psychiatric problems have mainly occurred in children, adults should watch children who are taking the drug to ensure that the drug is being tolerated well by the child.

Reports conclude that such side effects occur in less than 1% of people who take the drug. Additionally, some behavioral or neurological symptoms have been observed in patients infected with the Influenza virus. Therefore, it is hard to draw a conclusion on whether these problems are due to taking oseltamivir, or due to the infection itself. 

Less common side effects

Some less common side effects that have been reported in people taking oseltamivir include: 

  • Headache
  • Pain
  • Fatigue
  • Nosebleeds

This is not an exhaustive list of all the side effects that oseltamivir can have. If you experience any other unusual symptoms while taking the medication, report them to your doctor immediately. 

Allergic reactions 

As when taking any new medication, a serious allergic reaction could occur when taking oseltamivir for the first time. This is extremely rare, but symptoms of an allergic reaction should not be ignored.

Get emergency medical help if you experience the symptoms of a severe allergic reaction like hives, difficulty breathing or swallowing, swelling of the tongue or throat, or a severe skin reaction like a purple or red rash with blistering and peeling skin. 

Drug Interactions 

In general, oseltamivir is safe to be taken along with other medications and you probably will not need to adjust the timing or dose of any of your other medications when you take it. You should always tell your doctor and pharmacist about any other medication you may be taking though. This is in the case a rare drug interaction could occur with another medication you might be taking.

Drug interactions can also occur with other over-the-counter medications that you may be taking regularly, so be sure to inform your doctor and pharmacist if you are taking any of these medications too.  

How to purchase Oseltamivir 

If you are prescribed oseltamivir to prevent or treat the seasonal flu, it is important to take it exactly as prescribed by your doctor. The full course must also be completed even if you start to feel better before you finish the course. You can purchase oseltamivir by taking your prescription in with you to the pharmacy.

The cost of this drug can be quite high, especially for people without health insurance or with an insurance plan that does not cover prescription drugs. A prescription drug discount card can help save on oseltamivir. A convenient discount card is available from that provides savings on all FDA-approved drugs. The card is free and can be printed from the comfort of your home. Take the card in with you to the pharmacy when you are filling your prescription to get more than 50% savings on oseltamivir. Even if you have health insurance, the amount you will have to pay after applying the discount card could be cheaper than the copay amount. 

As anti-viral agents like oseltamivir are available to help shorten the duration of illness due to influenza, cost should not be a factor that prevents you from getting the medication. If you are part of any of the high-risk categories described above, the likelihood that oseltamivir is prescribed to you if you contract the flu will be higher than other individuals.

Understanding how the drug works, knowing what to expect when you take it, and exploring your options on how to save on the drug will all help you on your way to recovering quickly. 

We are committed to providing our readers with only trusted resources and science-based studies with regards to medication and health information. 

Disclaimer: This general information is not intended to diagnose any medical condition or to replace your healthcare professional. If you suspect medical problems or need medical help or advice, please talk with your healthcare professional.

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