Bimzelx (bimekizumab-bkzx) can cause side effects that range from mild to serious. More common side effects include headache and upper respiratory tract infection. If side effects from Bimzelx become difficult to tolerate, talk with your doctor about coping tips or other treatment options.

Bimzelx is used to treat the following conditions in certain adults:

The active ingredient in Bimzelx is bimekizumab-bkzx.* Bimzelx is a biologic drug, which means it’s made from parts of living cells.

Bimzelx comes as a liquid solution that you inject under your skin using a prefilled syringe or an auto-injector.

* The reason “-bkzx” appears at the end of the drug’s name is to show that the drug is distinct from similar medications that may be created in the future.

Some people may experience mild to serious side effects during Bimzelx treatment. The drug’s common side effects may vary depending on the condition it’s being used to treat. But a few examples of the commonly reported side effects include:

Note: Although Bimzelx itself does not cause viral, yeast, or other forms of infection, this drug can reduce your body’s ability to fight infection. This means treatment with this medication can increase your risk of acquiring certain conditions.

Mild side effects have been reported with Bimzelx. The drug’s side effects may vary depending on the condition it’s being used to treat. But examples of mild side effects include:

In most cases, these side effects should be temporary. And some may be easily managed with prescription or over-the-counter drugs. But if you have symptoms that are ongoing or bothersome, talk with your doctor or pharmacist. And do not stop treatment with Bimzelx unless your doctor recommends it.

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

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

* An allergic reaction is possible after injecting Bimzelx, but this side effect wasn’t reported in studies.

Serious side effects have been reported with Bimzelx. The drug’s side effects may vary depending on the condition it’s being used to treat. But examples of serious side effects include:

If you develop serious side effects during Bimzelx 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.

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

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 during treatment with Bimzelx and want to tell the FDA about it, visit MedWatch or call 800-FDA-1088.

* An allergic reaction is possible after injecting Bimzelx, but this side effect wasn’t reported in studies.

Get answers to some frequently asked questions about side effects of Bimzelx.

Does Bimzelx cause weight gain or weight loss?

No, Bimzelx is not known to cause weight gain or weight loss. In studies of the drug, changes in weight were not reported as a side effect.

However, certain side effects of Bimzelx, such as IBD and gastroenteritis, can decrease your appetite. This could lead to weight loss in some people. Bimzelx treatment may also raise your risk of infection, and decreased appetite can be a symptom of infection.

If you notice a decrease in your appetite or unexplained weight changes during your Bimzelx treatment, talk with your doctor. They can help determine the cause and talk about next steps if needed.

Does Bimzelx cause hair loss?

No, hair loss was not a side effect reported in studies of Bimzelx. However, folliculitis (swollen, infected hair follicles) was a mild side effect reported in these studies. Folliculitis can occur on your skin wherever hair grows, including your scalp.

A rare complication of folliculitis is permanent hair loss. If you’re concerned about hair loss with Bimzelx, talk with your doctor.

How long do side effects of Bimzelx usually last?

Injection site reactions usually resolve in a few days. Headaches may be short term and can often be treated with over-the-counter acetaminophen. If you have a chronic (long-term) headache or an injection site reaction lasting longer than 2 to 3 days, contact your doctor. These symptoms may require a medical evaluation.

Bimzelx suppresses your immune system, which can make you more susceptible to infections. These may last for a usual amount of time, or they may become chronic. Infections include:

  • oral or genital herpes
  • tuberculosis (TB)
  • upper respiratory tract, skin, or yeast infection

Most infections can be treated with prescription drugs, so letting your doctor know about an infection early on may make it easier to manage. Symptoms of a severe infection requiring prompt medical attention include:

Talk with your doctor or pharmacist to learn more about possible side effects of Bimzelx and how long they may last.

Does Bimzelx cause long-term side effects?

It’s possible. Long-term side effects include those that may start at any time during treatment with a drug, even if you’ve been injecting it for a long time. It also includes side effects that may not go away, even after you stop treatment with the drug.

Examples of long-term side effects reported in Bimzelx’s studies include:

  • chronic infection, such as:
    • mouth, skin, or genital yeast infection
    • upper respiratory tract infection
    • acne or infected hair follicles
    • herpes simplex of the mouth or genitals
  • nail or foot fungus
  • inflammatory bowel disease*
  • suicidal thoughts or behaviors
  • increased liver enzymes

If you’re concerned about possible long-term side effects from Bimzelx, talk with your doctor or pharmacist.

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

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

Injection site reaction

Injection site reactions were a common side effect reported in studies of Bimzelx. Injection site reactions may cause symptoms such as:

  • itching
  • a hard skin lump
  • warmth at the injection site
  • swelling
  • bruising or skin discoloration
  • pain or tenderness at the injection site

Factors that can increase the risk of injection site reactions with this drug include:

  • injecting Bimzelx that’s colder than room temperature
  • incorrect injection site or technique

What might help

If you have injection site reactions during Bimzelx treatment, the following tips may help prevent your symptoms:

  • Watch this video on the correct Bimzelx injection technique.
  • Avoid injecting into or near areas that have rashes, scars, or bruises.
  • Allow Bimzelx to sit at room temperature for 30 minutes before injecting it.
  • Avoid harsh rubbing of the injection site.
  • Apply a cool compress to a swollen, discolored injection site.

If you have an injection site reaction lasting longer than 2 to 3 days, contact your doctor, as these symptoms may need a medical evaluation.

Inflammatory bowel disease

Inflammatory bowel disease (IBD) was an uncommon but serious side effect reported in studies of Bimzelx. IBD may cause symptoms such as:

Factors that can increase the risk of developing IBD with Bimzelx treatment include:

  • viral or bacterial infection
  • personal or family history of IBD
  • smoking
  • diet high in saturated fats and processed foods
  • being younger than 35 years old
  • belonging to a certain ethnic group, such as white, Ashkenazi Jew, or Black
  • having a sedentary lifestyle or job
  • living in a cold climate or urban setting

What might help

If you have symptoms of IBD during Bimzelx treatment, talk with your doctor right away. They’ll likely recommend an urgent medical evaluation.

Allergic reaction

Like most drugs, Bimzelx can cause an allergic reaction in some people, but this side effect wasn’t reported in studies. Symptoms can be mild to serious and can include:

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

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. Examples include:

  • an oral antihistamine, such as diphenhydramine (Benadryl)
  • a product you apply to your skin, such as hydrocortisone cream

If your doctor confirms you’ve had a mild allergic reaction to Bimzelx, they’ll decide whether you should continue treatment with it.

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

The following is important information you should consider before starting Bimzelx treatment.

Warnings

Bimzelx can sometimes cause harmful effects in people with certain conditions. This is known as a drug-condition interaction. Other factors may also affect whether Bimzelx is a good treatment option for you.

Talk with your doctor about your health history before starting treatment with this medication. Be sure to tell them if any of the following factors apply to you:

  • history of depression, or suicidal thoughts or behavior
  • history of TB or other active or chronic (long-term) infection
  • liver problems
  • live vaccine received within the past 14 days
  • history of IBD
  • past allergic reaction to Bimzelx
  • pregnancy
  • breastfeeding
  • alcohol consumption

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.