Olumiant’s most common side effects include upper respiratory infection, high liver enzyme levels, headache, and nausea.

Olumiant (baricitinib) is approved to treat the following conditions in adults:

Keep reading to learn about the common, mild, and serious side effects that Olumiant can cause. For details about this drug’s uses and other information, see this Olumiant overview.

Olumiant has boxed warnings. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). For details, see the “Boxed warnings for Olumiant” section.

Examples of commonly reported side effects of Olumiant include:

These are just a few of the side effects Olumiant may cause, but side effects won’t happen to everyone. Read on to learn more about mild to serious side effects of Olumiant.

Examples of mild side effects reported with Olumiant include:

  • upper respiratory infection (URI)
  • nausea

To learn more about these side effects, see the “Side effects explained” section.

In most cases, these side effects should be temporary. And some may be easily managed. But if you have symptoms that are ongoing or that bother you, talk with your doctor or pharmacist. And don’t stop using Olumiant unless your doctor recommends it.

Olumiant may cause mild side effects other than the ones listed previously. See the Olumiant prescribing information for details.

Treatment with Olumiant can cause serious side effects, but they aren’t common. Serious side effects reported with Olumiant include:

To learn more about some of these side effects, see the “Side effects explained” and “Boxed warnings for Olumiant” sections.

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

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. Sharing your experience helps make medication safer for everyone by giving doctors and researchers more information about how the drug works in real life. If you develop a side effect while taking Olumiant and want to tell the FDA about it, visit MedWatch or call 800-FDA-1088.

While rare, treatment with Olumiant can cause long-term side effects. These side effects may start during treatment but continue for a long time, possibly after treatment has stopped.

Long-term side effects reported by people taking Olumiant in studies include:

Olumiant has boxed warnings about the risk of these side effects. This is the most serious warning from the Food and Drug Administration (FDA).For more information about these side effects, see the “Boxed warnings for Olumiant” section.

You can also talk with your doctor or pharmacist to learn more about potential long-term side effects from Olumiant therapy.

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

Is it possible to have weight gain from taking Olumiant?

Maybe. In studies, weight gain was reported as a side effect by people taking Olumiant for alopecia areata. But this symptom wasn’t reported by people taking the drug to treat rheumatoid arthritis (RA) or COVID-19.

Certain other medications used to treat RA, including corticosteroids such as prednisone (Rayos), can cause weight gain.

Keep in mind that RA, which Olumiant is used to treat, can cause symptoms such as joint pain. This can make it hard to be physically active, which can lead to weight gain in people with RA. Olumiant helps make RA symptoms less severe, which can make it easier to exercise.

If you’re concerned about weight gain and your treatment plan, talk with your doctor. They can suggest ways to maintain a weight that’s right for you.

Will Olumiant cause hair loss?

No, it’s not expected to. In fact, Olumiant is approved to treat hair loss due to alopecia areata, which causes hair loss that can affect your entire body.

Hair loss isn’t a side effect reported in studies of Olumiant. But RA, which Olumiant is used to treat, may cause hair loss. Other medications that treat RA can also cause hair loss as a side effect, including:

Talk with your doctor if you’re concerned about hair loss with Olumiant treatment.

Are patient reviews available for Olumiant?

Olumiant’s manufacturer provides patient stories on its website, and other reviews may be available online. Keep in mind that each person’s experience with the drug can be different. Your doctor or pharmacist may also be able to tell you about other people’s experiences with Olumiant.

Is there a 4-mg dose of Olumiant? If so, are there any side effects specific to it?

Yes, Olumiant comes in a strength of 4 milligrams (mg). Olumiant can be prescribed in a 4-mg dose for some conditions. Side effects of a 4-mg dose are expected to be similar to those caused by a 2-mg dose.

An Olumiant dosage of 4 mg taken once per day is recommended for severe COVID-19. A 4-mg dose can be prescribed for severe alopecia areata as well. A 4-mg dose isn’t usually prescribed for RA, however.

Be sure to follow the Olumiant dosage your doctor prescribes for you.

Does Olumiant weaken your immune system?

Olumiant works by reducing certain activities of your immune system, referred to as weakening of the immune system. This can help reduce inflammation in your body, further decreasing the symptoms of the conditions Olumiant treats.

Specifically, Olumiant is a Janus kinase (JAK) inhibitor drug, which blocks a protein called Janus kinase. This protein acts as a messenger between other proteins and cells in your immune system. Blocking Janus kinase stops messages between the immune system cells that cause inflammation.

See the “Serious infections” section for details about the risk of infection with Olumiant and how you and your doctor can manage this.

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

Nausea

Nausea was one of the more common side effects in people taking Olumiant for RA or alopecia areata in studies. Sometimes nausea can go away after a few days, weeks, or months, as your body gets used to Olumiant.

What might help

If you have nausea during Olumiant treatment, be sure to discuss this with your doctor. Some ways to manage or help prevent nausea include:

  • taking over-the-counter medications, such as scopolamine
  • following the BRAT diet (bananas, rice, applesauce, and toast) until your stomach is more settled
  • staying hydrated by taking small, frequent sips of water or another beverage
  • eating small, frequent meals

Upper respiratory infection

Upper respiratory infection is one of the more common side effects in people taking Olumiant for RA or alopecia areata in studies. These infections can include the common cold or a sinus infection. Because Olumiant works by reducing immune system activity, you’re more likely to get infections like this during treatment.

Symptoms can include:

  • fever or chills
  • cough
  • runny or congested nose
  • sore throat

What might help

If you have mild or moderate symptoms, your doctor may recommend an over-the-counter cold medication. If you have severe symptoms, be sure to discuss this with your doctor so they can recommend treatment.

To help prevent infections, be sure to wash your hands often, and make sure you’re up to date on all your vaccinations.

Allergic reaction

For some people, Olumiant can cause an allergic reaction. In general, symptoms of an allergic reaction can be mild or serious.

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 continue Olumiant treatment.

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 Olumiant, they may have you switch to a different treatment.

Olumiant has several boxed warnings. Boxed warnings are the most serious warning a drug can be given by the Food and Drug Administration (FDA).

Serious infections

Olumiant has a boxed warning about increasing your risk of infection. In rare cases, this can include serious or life threatening infections, such as pneumonia and shingles.

Olumiant works by reducing the activity of your immune system, which is why it increases your risk of infection.

Symptoms of infection can vary depending on the type, and can include:

Other medications you take, including other medications that treat rheumatoid arthritis (RA), can also increase your risk of infection. These include methotrexate (Trexall, Otrexup, Rasuvo) and corticosteroids, such as prednisone (Rayos).

Certain people are at higher risk of infection if they take Olumiant. This includes people who have:

  • a long-term or recurrent infection
  • been exposed to tuberculosis (TB) or lived somewhere with widespread TB
  • lived or traveled to places with a higher risk of certain fungal infections
  • certain medical conditions that weaken the immune system

Taking Olumiant can reactivate certain bacteria and viruses if you’ve been exposed to them before. (When bacteria or viruses are reactivated, it causes symptoms of infection after not causing any for a long time.) Bacteria and viruses that may be reactivated by taking Olumiant include:

What might help

Before prescribing Olumiant, your doctor will likely test you for tuberculosis. They may also check you for other infections. If these tests are active, your doctor will likely want to treat the infection before prescribing Olumiant.

Before starting Olumiant treatment, be sure to tell your doctor if you have:

  • any active infections
  • any of the risk factors for infections mentioned earlier

Your doctor will use this information to help decide if Olumiant is safe for you to take.

While taking Olumiant, your doctor will closely watch you for any signs of infection. If you develop symptoms of an infection, contact your doctor right away. They’ll want to see you and order tests to confirm. If the tests are positive, they’ll prescribe treatment, such as an antibiotic or antifungal.

If you develop an infection during Olumiant treatment, your doctor may have you stop taking the drug temporarily. Your doctor will then wait until the infection clears before having you resume treatment with Olumiant.

Cancer

Although extremely rare, several people developed certain cancers while taking medications similar to Olumiant in studies. Because Olumiant is similar to these medications, the drug has a boxed warning about this side effect.

Specifically, you may be at increased risk of developing lymphoma, a type of blood cancer. People who smoke or previously smoked have an increased risk of cancer, including lung cancer, with Olumiant or similar drugs.

Also, people taking Olumiant in studies had a higher risk of developing nonmelanoma skin cancers.

Because Olumiant works by reducing the activity of your immune system, it increases the risk of developing certain cancers.

What might help

Before starting Olumiant, be sure to discuss with your doctor any medical conditions you have and medications you take. Your doctor will use this information to help determine your risk of developing cancer and whether Olumiant is safe for you.

Blood clots

While very rare, some people developed blood clots while taking Olumiant in studies. This drug has a boxed warning about this side effect.

Clots reported by people taking Olumiant include:

Symptoms of a blood clot can include:

What might help

Call your doctor right away or seek emergency care if you notice symptoms of a blood clot while taking Olumiant. These blood clots can be life threatening and require treatment in a hospital.

Serious cardiovascular problems

Although rare, several people developed certain cardiovascular (heart and blood vessel) problems while taking medications similar to Olumiant in studies. Because Olumiant works in a similar way to the drugs in the study, it has a boxed warning about this side effect.

Cardiovascular problems caused by Olumiant and drugs like it include heart attack and stroke.

Symptoms of a heart attack can include:

Symptoms of a stroke can include sudden:

  • numbness or weakness in your arm, face, or leg, especially on one side of your body
  • speech problems, such as trouble speaking
  • difficulty walking or coordination problems
  • vision problems, such as difficulty seeing out of one eye

If you smoke or have smoked in the past, you’re at higher risk of serious cardiovascular problems if you take Olumiant. You’re also at higher risk if you already have risk factors for cardiovascular problems, such as:

What might help

If you notice symptoms of a serious cardiovascular problem, including heart attack or stroke, while taking Olumiant, call your doctor right away and seek emergency medical care.

Before you begin Olumiant, your doctor will discuss with you the risks and benefits of this medication. This should include a discussion about your risk of serious cardiovascular problems.

If your doctor prescribes Olumiant to you, they’ll monitor your cardiovascular health. And they’ll have you stop taking Olumiant if you have a serious cardiovascular problem during treatment.

Increased risk of death

Olumiant has a boxed warning about increased risk of death in certain people. This is because certain people taking a drug similar to Olumiant in a study had a higher risk of death compared with other medications used to treat rheumatoid arthritis. Because the drugs work in a similar way, Olumiant has a boxed warning about this side effect.

Specifically, people over the age of 50 years who had at least one risk factor for cardiovascular problems were at increased risk of death in this study. (See the “Serious cardiovascular problems” section.)

What might help

Your doctor will discuss with you the risks and benefits of taking Olumiant. If they prescribe this medication for you, they may monitor your health closely during treatment. Your doctor will talk with you about your health and any risks you may have from Olumiant treatment.

When considering treatment with Olumiant, it’s important to discuss your overall health with your doctor.

It’s important to note that Olumiant has several boxed warnings. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). For details, see the “Boxed warnings for Olumiant” section.

Other precautions

Olumiant may not be right for you if you have certain medical conditions or other factors that affect your health. Talk with your doctor about your health history before starting Olumiant. Factors to consider include:

  • any infection that’s active (causing symptoms)
  • any factors that put you at increased risk of infection prior to starting Olumiant treatment
  • diverticulitis
  • ulcers in your intestines or stomach
  • kidney problems, including chronic kidney disease
  • liver problems, such as hepatitis B or hepatitis C
  • history of tuberculosis
  • allergic reaction to Olumiant or any of its ingredients
  • alcohol consumption
  • pregnancy and breastfeeding (see the following section)

Pregnancy and breastfeeding while taking Olumiant

It’s not known whether Olumiant is safe to take while pregnant. Talk with your doctor if you’re pregnant or thinking of becoming pregnant before you take Olumiant.

It is also not known whether Olumiant passes into human breast milk. But due to the potential risk of side effects, your doctor will likely recommend that you don’t breastfeed while taking Olumiant. They can recommend safe feeding options for your child.

Q:

Are there lab tests my doctor will order to check for side effects if I begin taking Olumiant?

Anonymous

A:

Yes, your doctor may give you lab tests to check for side effects with Olumiant.

Here are a few tests your doctor may order to check for side effects of the drug:

If you’ve had certain infections in the past, Olumiant may reactivate them. This means you may have symptoms of these conditions again after not having any for a long time. In this case, your doctor may give you tests to check for these infections before you start the drug. Examples include tuberculosis and hepatitis.

If you have questions about lab tests you’ll need with Olumiant, talk with your doctor.

The Healthline Pharmacist TeamAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.

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.