Kesimpta (ofatumumab) is a brand-name prescription medication. The Food and Drug Administration (FDA) has approved it to treat certain forms of multiple sclerosis (MS) in adults, which include:

Here are some fast facts about Kesimpta:

If you and your doctor decide that Kesimpta is working well to treat your condition, you’ll likely take it long term.

As with other drugs, Kesimpta can cause side effects. Read on to learn about potential common, mild, and serious side effects. For a general overview of Kesimpta, see this article.

Kesimpta can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported by people who took Kesimpta in clinical trials:

* For more information about this side effect, see “Side effect specifics” below.

Mild side effects can occur with Kesimpta use. This list doesn’t include all possible mild side effects of the drug. For more information, you can refer to Kesimpta’s prescribing information.

Mild side effects that have been reported with Kesimpta include:

These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you develop a side effect during Kesimpta treatment and want to tell the FDA about it, visit MedWatch.

* For more information about this side effect, see “Side effect specifics” below.

Kesimpta may cause rare and serious side effects. The list below may not include all possible serious side effects of the drug. For more information, you can refer to Kesimpta’s prescribing information.

If you develop serious side effects during Kesimpta treatment, 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.

Serious side effects that have been reported and their symptoms include:

* For more information about this side effect, see “Side effect specifics” below.
† An allergic reaction is possible after injecting Kesimpta. However, this side effect wasn’t reported in clinical trials. To learn more, see the “Side effect specifics” section below.

Kesimpta may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.

Will I have hair loss with Kesimpta?

Hair loss was not reported as a side effect of Kesimpta in clinical trials of the drug.

However, hair thinning and hair loss have been reported to a Food and Drug Administration (FDA) database by people having other multiple sclerosis (MS) treatments. These reports are voluntary and do not include each person’s full medical history. This means it’s not known for sure that the MS treatments caused the hair loss. It’s also not possible to determine how common this side effect is.

If you are concerned about hair loss, talk with your doctor. They can suggest ways to help prevent or manage hair loss.

Which lab tests will I need to have done before starting Kesimpta treatment?

You will need to have certain lab tests done before and during Kesimpta treatment.

Before you start Kesimpta, you will have a blood test to check for an active or past hepatitis B virus (HBV) infection. The HBV test is done before starting Kesimpta because the drug weakens your immune system’s ability to fight infections. If you have had HBV in the past, this treatment may cause reactivation (in which the virus becomes active again) of the infection.

HBV reactivation was not seen in clinical trials of Kesimpta for treating MS. However, HBV reactivation did occur in people taking ofatumumab (the active drug in Kesimpta) in clinical trials involving people with chronic lymphocytic leukemia.

If your test is positive for HBV, your doctor may recommend another MS treatment option for you. If they recommend that you start Kesimpta despite the positive test result, they may monitor your liver function on a routine basis.

Symptoms of HBV include abdominal pain, diarrhea, and jaundice. In severe cases, HBV can cause liver damage and liver failure. If you experience these symptoms during Kesimpta treatment, talk with your doctor right away. They can recommend whether it’s safe to continue Kesimpta treatment.

Learn more about some of the side effects that Kesimpta may cause. To find out how often side effects occurred in clinical trials, see the prescribing information for Kesimpta.

Injection-related side effects

Injection-related reactions may occur with Kesimpta. These reactions were common in clinical trials of Kesimpta.

Injection-related reactions are body-wide reactions that often happen within the first 24 hours after your injection. They are more common with the first injection (first dose of Kesimpta) compared with subsequent injections.

Symptoms of an injection-related reaction are typically mild to moderate. They can include:

Because an injection-related reaction is most likely to happen with your first injection of Kesimpta, you will receive the first dose at your doctor’s office or clinic. This allows them to monitor for a reaction. They can then provide support and treatment, if needed.

If you have an injection-related reaction after giving yourself a dose of Kesimpta, call your doctor right away. If you feel you are having a medical emergency, immediately call 911 or your local emergency number.

Injection site reactions

Injection site reactions were reported in clinical trials of Kesimpta involving people with multiple sclerosis (MS). These reactions were common in clinical trials of Kesimpta.

Injection site reactions occur near the area of the injection. These reactions are typically mild or moderate and go away within a few days. Symptoms of injection site reactions may include:

  • itching
  • pain
  • swelling
  • skin discoloration

If you experience these symptoms for longer than a few days or they are bothersome, talk with your doctor. They can recommend ways to relieve your symptoms and help prevent or lessen them in the future.

Low levels of immunoglobulins

Low levels of immunoglobulins occurred in clinical trials of Kesimpta. This side effect was common in clinical trials of Kesimpta. Immunoglobulins are a type of antibody protein produced by your immune system. They work to detect and fight bacteria and viruses in order to help prevent infections.

When levels of immunoglobulins are too low, your immune system is not able to fight off infections as effectively. This can lead to more frequent or more severe infections.

Symptoms of low immunoglobulins can include:

  • fever
  • skin rash
  • frequent infections

What you can do

Before starting Kesimpta, talk with your doctor about any current or chronic (long-term) infections you have. If you have a current infection, they may recommend that you wait until the infection is resolved before starting Kesimpta treatment.

If you develop an infection during Kesimpta treatment, tell your doctor. They will decide whether it’s safe to continue the medication.

Your doctor may also monitor your immunoglobulin levels with blood tests. This will help them determine your risk of infection and the safety of the medication for you.

Infections, including serious infections

Serious infections may occur during Kesimpta treatment. This is because Kesimpta reduces your MS symptoms by lowering your immune system’s activity.

Since your immune system is weakened during treatment, it is not able to fight off infection as well. This increases your risk of both mild and serious infections. Mild infections were very common in clinical trials of Kesimpta, while serious infections were less common.

In Kesimpta’s clinical trials, people experienced common mild infections. These infections included:

There is also a risk of uncommon, more serious infections during Kesimpta treatment that may require hospitalization. An example of a very rare, serious infection is progressive multifocal leukoencephalopathy (PML). This is a brain infection caused by the John Cunningham (JC) virus.

There were no cases of PML in clinical trials of Kesimpta. However, the infection was reported in clinical trials of the drug’s active ingredient (ofatumumab) in people with chronic lymphocytic leukemia. It’s also been reported in people receiving different antibody treatments and other MS treatments.

Most adults have the JC virus in their bodies. However, a healthy immune system typically prevents the virus from causing illness. Because Kesimpta causes a weakened immune system, the JC virus could be reactivated and cause a severe brain infection.

Symptoms of PML include general weakness on one side of the body that progressively gets worse, difficulty speaking, memory problems, and personality changes.

What you can do

If you experience symptoms of a mild infection, such as the common cold, tell your doctor. They may want to monitor your symptoms and check that the infection goes away. If your immune system is not able to fight off a mild infection, your doctor will discuss with you the risks and benefits of continuing Kesimpta treatment.

If you have symptoms of a more severe infection, including those described above for PML, talk with your doctor immediately. They may recommend that you stop Kesimpta treatment. If you feel you are having a medical emergency, immediately call 911 or your local emergency number.

Allergic reaction

As with most drugs, Kesimpta can cause an allergic reaction in some people. However, this side effect wasn’t reported in clinical trials.

Symptoms can be mild or serious and can include:

  • skin rash
  • itching
  • flushing
  • swelling under your skin, typically in your eyelids, lips, hands, or feet
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

What you can do

For mild symptoms of an allergic reaction, call your doctor right away. They may recommend ways to ease your symptoms and determine whether you should continue Kesimpta treatment. However, if your symptoms are serious and you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Be sure to talk with your doctor about your health history before you start treatment with Kesimpta. This drug may not be the right treatment option for you if you have certain medical conditions or other factors that affect your health. These are known as drug-condition or drug-factor interactions.

The conditions and factors to consider include:

Hepatitis B. If you have an active hepatitis B virus (HBV) infection, your doctor will likely not prescribe this drug for you. Talk with your doctor if you have a history of HBV or have a current infection. Kesimpta may lead to a reactivation of HBV in your body. Your doctor will order lab tests to determine whether Kesimpta is safe for you. They may recommend HBV treatment before you start Kesimpta, if needed.

Active infection. If you have an active infection (in addition to HBV), your doctor will likely wait until the infection has resolved before prescribing Kesimpta for you. Talk with your doctor about your history of infections and any current or chronic (long-term) infections you have. Kesimpta can make it harder for your body to fight infections, so you may need treatment for an active infection before starting treatment with Kesimpta.

Pregnancy. It’s not known whether Kesimpta treatment is safe during pregnancy. If you are considering becoming pregnant or are pregnant, talk with your doctor. They will discuss the risks and benefits of Kesimpta treatment during pregnancy. For more information, see the “Pregnancy and breastfeeding with Kesimpta” section below.

Breastfeeding. It’s not known whether Kesimpta treatment is safe while breastfeeding. If you are breastfeeding or considering it, talk with your doctor. They can discuss the risks and benefits of breastfeeding during Kesimpta treatment. For more information, see the “Pregnancy and breastfeeding with Kesimpta” section below.

Recent vaccination. Tell your doctor about any recent vaccinations that you’ve had before you start Kesimpta. They may recommend that you wait a few weeks after your last vaccine before starting treatment with this drug.

Certain vaccines contain living or weakened versions of a bacteria or virus. These are called live or live-attenuated vaccines. Since Kesimpta may weaken your immune system, the vaccine could cause an actual infection. It’s recommended to wait at least 4 weeks for live or live-attenuated vaccines, and at least 2 weeks for inactivated vaccines, if possible.

Allergic reaction. If you’ve had an allergic reaction to Kesimpta or any of its ingredients, your doctor will likely not prescribe Kesimpta. Ask your doctor what other medications may be better options for you.

Alcohol with Kesimpta

There are no known interactions between alcohol and Kesimpta. However, drinking alcohol may make some of your multiple sclerosis (MS) symptoms worse, including difficulty walking and changes in vision. This is because alcohol also has these effects on the body.

Talk with your doctor to learn whether alcohol is safe to consume during treatment with Kesimpta.

Pregnancy and breastfeeding with Kesimpta

It’s not known whether Kesimpta treatment is safe during pregnancy. In animal studies, offspring of pregnant animals that received Kesimpta were born with weakened immune systems. This harmful effect was also reported in human infants born to people who received drugs that work in a similar way to Kesimpta.

If you’re able to become pregnant, your doctor will recommend using effective birth control during Kesimpta treatment and for at least 6 months after your last dose of Kesimpta. If you are pregnant and considering Kesimpta, talk with your doctor about the risks and benefits of this drug.

It’s also not known whether Kesimpta treatment is safe while you’re breastfeeding. There are no clinical trials to test the effects of Kesimpta on breast milk production or what effects the drug may have on a child who is breastfed. If you are breastfeeding or considering it, talk with your doctor to learn whether Kesimpta is a safe option for you.

Several common and mild side effects are possible with Kesimpta. They typically go away within a few days. Serious side effects may also be possible, though these are rare. Talk with your doctor about your medical history before starting Kesimpta treatment. They will discuss the risks and benefits of Kesimpta for your condition.

If you’d like to learn more about Kesimpta, talk with your doctor or pharmacist. They can help answer any questions you have about side effects from the drug.

Besides talking with your doctor, you can do some research on your own. These articles might help:

  • More information about Kesimpta. For details about other aspects of Kesimpta, refer to this article.
  • Cost. If you’d like to learn about Kesimpta and cost, refer to this article.
  • Dosage. For information about the dosage of Kesimpta, view this article.
  • A look at multiple sclerosis (MS). For details about your condition, see our MS hub.

Disclaimer: Medical News Today 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.