If you have rheumatoid arthritis (RA), you may be interested in learning more about leflunomide. It’s a generic prescription drug used to treat RA in adults.

Leflunomide comes as a tablet that you swallow. If you and your doctor decide that this drug is safe and effective for you, you’ll likely take it long term.

This article describes leflunomide’s side effects. For more information about this drug, including details about its uses, see this in-depth article.

Some people may experience mild to serious side effects during their leflunomide treatment. Examples of the drug’s commonly reported side effects include:

* To learn more about this side effect, see “Leflunomide’s side effects explained” below.
† Leflunomide has a boxed warning for this side effect. This is the most serious warning from the Food and Drug Administration (FDA). To learn more, see “Leflunomide’s side effects explained” below.

Many common side effects of leflunomide are mild. Examples that have been reported with this drug include:

* To learn more about this side effect, see “Leflunomide’s side effects explained” below.
† An allergic reaction is possible after using leflunomide. But it’s not clear whether this side effect occurred in studies.

In most cases, these side effects should be temporary. And some may be easily managed. But if you have symptoms that are ongoing or bother you, talk with your doctor or pharmacist. And do not stop taking leflunomide unless your doctor recommends it.

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

Many common side effects of leflunomide are mild and go away on their own. But some people may have serious side effects that could require medical attention.

Serious side effects that have been reported with this drug include:

If you develop serious side effects while taking leflunomide, 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.

* Leflunomide has a boxed warning for this side effect. This is the most serious warning from the Food and Drug Administration (FDA). To learn more, see “Leflunomide’s side effects explained” below.
† Leflunomide has a boxed warning for this side effect. This is the most serious warning from the FDA. To learn more, see the “Leflunomide warnings” section below.
‡ To learn more about this side effect, see “Leflunomide’s side effects explained” below.
§ An allergic reaction is possible after taking leflunomide. But it’s not clear whether this side effect occurred in studies.

Note: After the FDA approves a drug, it tracks side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with leflunomide, visit MedWatch.

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

Is there a difference in side effects between the 10-mg and 20-mg strengths of leflunomide?

It’s possible. Although leflunomide side effects can happen with any dosage, your risk of certain side effects may increase with a higher dose.

For example, the risk of increased liver enzyme levels may be higher with a leflunomide 20-milligram (mg) dose than with a 10-mg dose. Elevated liver enzyme levels could be a sign of liver damage, which leflunomide has a boxed warning for. (See the “Side effects explained” section below for details.)

Keep in mind that the recommended dosage of leflunomide is 20 mg once daily. But if you have liver-related side effects, your doctor may decrease your dosage to 10 mg once daily.

Talk with your doctor if you have concerns about the risk of side effects with your leflunomide dosage.

Can leflunomide affect bowel movements?

Yes. In leflunomide studies, diarrhea was one of the more commonly reported side effects. (With diarrhea, you may experience frequent urges to have bowel movements. And you may have large volumes of stool with your bowel movements. Your stool may also be softer than usual or watery.)

Talk with your doctor or pharmacist if you have bothersome problems with your bowel movements while taking this drug. They can recommend over-the-counter treatments or other ways to manage this side effect.

Does stopping leflunomide cause side effects, such as withdrawal symptoms?

No, stopping leflunomide should not cause withdrawal symptoms.

It can take up to 2 years for leflunomide to be completely cleared from your body after you stop taking it. Because of this, your doctor will likely have you take other medications to help clear your system faster after you stop leflunomide. But this process isn’t meant to prevent withdrawal symptoms.

Keep in mind that symptoms of rheumatoid arthritis, which leflunomide treats, may come back if you stop taking the drug.

Always be sure to take leflunomide exactly as your doctor prescribes. And do not stop taking it without their recommendation. If you’d like to stop the drug, talk with your doctor first. They’ll recommend a safe way for you to do so.

Is weight gain a side effect of leflunomide?

No. Weight gain was not reported as a side effect in leflunomide studies. Instead, people taking leflunomide reported side effects such as loss of appetite, nausea, and vomiting. Having these side effects could make it difficult to eat, which may result in weight loss.

Talk with your doctor if you have concerns about weight changes while taking leflunomide.

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

Risk of liver damage

Leflunomide has a boxed warning for the risk of liver damage. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). It alerts doctors and patients about drug effects that may be dangerous.

In leflunomide studies, a high level of liver enzymes was among the more common side effects in people taking this drug. And high liver enzymes can be a sign of liver toxicity or liver damage.

Symptoms of liver toxicity or liver damage can include:

  • nausea
  • loss of appetite
  • jaundice (yellowing of your skin or the whites of your eyes)
  • weight loss
  • fluid buildup in your belly or legs

In studies, most people with high liver enzymes saw a return to their usual levels after stopping leflunomide treatment or having their dose lowered.

What might help

Let your doctor know if you have liver problems or have had them in the past. Before prescribing leflunomide, your doctor will do a blood test to measure your liver enzyme levels. They’ll also check them regularly throughout your treatment. If your liver enzyme levels are too high, your doctor may decrease your dosage or have you stop taking leflunomide.

Due to the risk of liver damage, your doctor will likely not prescribe this drug for you if you have liver problems.

Contact your doctor immediately if you have symptoms of liver toxicity or liver damage. They’ll try to determine the cause of your symptoms. If they confirm that you have liver damage, they’ll have you stop taking leflunomide. They’ll also have you take medication to clear the drug from your body more quickly.

Hair loss

Hair loss was a common side effect in leflunomide studies. But keep in mind that rheumatoid arthritis (RA), which this drug is used to treat, can also cause hair loss. So hair loss may be due to the leflunomide or the RA.

What might help

Treating your hair gently while taking leflunomide might help reduce hair loss. A few tips that may also help protect your hair include:

  • using mild and fragrance-free shampoo and conditioner when washing your hair
  • avoiding hot water when washing and rinsing your hair
  • limiting your hair washing to no more than two times per week
  • patting your hair dry after you’ve washed it instead of rubbing or scrubbing it
  • using a soft hairbrush or wide-tooth comb to gently brush or comb your hair
  • avoiding hot styling tools that may damage your hair, such as curling irons and straighteners

Talk with your doctor if you have bothersome hair loss while taking leflunomide. They can determine the cause and recommend other ways to help manage this side effect.

Eye-related side effects

Eye-related side effects occurred in leflunomide studies, but they weren’t common.

These included ocular (eye) problems, such as:

Symptoms may vary based on the kind of ocular problem, but general symptoms of eye-related side effects can include:

  • vision changes
  • seeing flashes of light or floaters
  • nausea or vomiting
  • unusual headaches

What might help

Let your doctor know right away if you have any symptoms of ocular problems while taking leflunomide. They can examine your eyes to determine the cause. If they find that you have a serious eye condition, they’ll likely have you stop taking leflunomide and treat the eye condition.

It’s important to tell your doctor as soon as you notice any eye-related side effects. In many cases, these vision problems go away completely when they’re treated early.

Skin reactions

Although it was rare in studies, taking leflunomide can cause serious skin reactions. These include:

Symptoms of these skin reactions can include:

What might help

Stevens-Johnson syndrome, TEN, and DRESS are medical emergencies. Call 911 or a local emergency number immediately if you have symptoms of any serious skin reaction while taking leflunomide.

Allergic reaction

Like most drugs, leflunomide can cause an allergic reaction in some people. But it’s not clear whether this side effect occurred in studies. Symptoms can be mild to serious and can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)
  • 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 antihistamine you swallow, such as Benadryl (diphenhydramine)
  • a product you apply to your skin, such as hydrocortisone cream

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

If you have symptoms of a severe allergic reaction, such as swelling or trouble 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 leflunomide, they may have you switch to a different treatment.

Keeping track of side effects

During your leflunomide treatment, consider taking notes on any side effects you’re having. You can then share this information with your doctor. This is especially helpful when you first start taking a new drug or using a combination of treatments.

Your side effect notes can include things such as:

  • what dose of the drug you were taking when you had the side effect
  • how soon you had the side effect after starting that dose
  • what your symptoms were
  • how it affected your daily activities
  • what other medications you were taking
  • any other information you feel is important

Keeping notes and sharing them with your doctor will help them learn more about how leflunomide affects you. They can then use this information to adjust your treatment plan if needed.

Leflunomide comes with several warnings, including two boxed warnings.

Boxed warnings

Leflunomide has boxed warnings about the risk of liver damage and the risk of harm if taken during pregnancy. Boxed warnings are the most serious warnings from the Food and Drug Administration (FDA). They alert doctors and patients about effects of a drug that may be dangerous.

Risk of liver damage. Leflunomide can cause serious, sometimes life threatening, liver damage. This risk is higher if you already have liver problems or take other medications that may cause liver damage.

Risk of harm if used during pregnancy. Leflunomide can cause harm to a developing fetus if taken during pregnancy. Due to this risk, you should not take leflunomide if you’re pregnant.

For details on liver damage, see “Leflunomide’s side effects explained” above. For more information on the risks if used while pregnant, see “Pregnancy and breastfeeding while taking leflunomide” below.

Other warnings

Leflunomide may not be right for you if you have certain medical conditions. This is known as a drug-condition interaction. Other factors can also affect whether leflunomide is a good treatment option for you. Talk with your doctor about your health history before starting this drug. Factors to consider include those described below.

Weakened immune system. Your doctor may not prescribe leflunomide for you if you have a weakened immune system. This is because the drug can increase your risk of serious infection, including tuberculosis. Having a weakened immune system also increases this risk. Before starting leflunomide, tell your doctor if you have a weakened immune system. They’ll likely recommend a different treatment option for you.

Allergic reaction. If you’ve had an allergic reaction to leflunomide or any of its ingredients, your doctor will likely not prescribe it for you. Ask them about other medications that might be better options.

Lung problems. Leflunomide can cause lung problems, such as swelling or scarring in the lungs. If you already have these lung problems, this drug can worsen them. Be sure to tell your doctor if you have any lung problems before starting leflunomide. They’ll likely recommend a different treatment option for your rheumatoid arthritis (RA).

High blood pressure. Be sure to tell your doctor if you have high blood pressure before you start taking leflunomide. This drug can cause high blood pressure or increase your blood pressure even more if you already have it. Your doctor will let you know if leflunomide is safe for you to take.

Active infection. Let your doctor know if you have any active infections before starting leflunomide. They’ll likely treat your infection before starting you on this drug.

Alcohol and leflunomide

There are no known interactions between alcohol and leflunomide. But drinking large amounts of alcohol can increase your risk of liver damage,* which is a dangerous potential side effect of leflunomide. So consuming a lot of alcohol while taking this drug can increase your risk of liver damage even more.

If you drink alcohol, talk with your doctor about how much, if any, is safe to consume with this drug.

* Leflunomide has a boxed warning for this side effect. This is the most serious warning from the Food and Drug Administration (FDA). For more details, see “Leflunomide’s side effects explained” above.

Pregnancy and breastfeeding while taking leflunomide

Below is information about taking leflunomide while pregnant or breastfeeding.

Risk of harm if used during pregnancy

It is not safe to take leflunomide during pregnancy. This drug has a boxed warning for the risk of harm to a fetus if taken during pregnancy. A boxed warning is the most serious warning from the Food and Drug Administration (FDA).

Due to this risk, your doctor will have you take a pregnancy test before prescribing leflunomide for you. And they’ll only prescribe this drug if the test is negative.

If you can become pregnant, you should use an effective form of birth control while taking leflunomide. And you may need to continue using birth control for up to 2 years after you stop treatment with this drug.

Tell your doctor right away if you become pregnant while taking leflunomide. They’ll have you stop taking the drug and give you treatments to help your body clear it more quickly.

Leflunomide and breastfeeding

It’s not known whether leflunomide passes into breast milk or what effects it would have on a breastfed child or milk production. But due to the risk of serious side effects on a breastfed child, it’s not recommended that you breastfeed while taking this drug.

Let your doctor know if you’re breastfeeding or planning to do so before starting leflunomide. They’ll recommend safe ways to feed your child or suggest a different treatment option for your RA.

If you have any questions about side effects that leflunomide can cause, talk with your doctor. You can also ask them about Arava, which is the brand-name* version of leflunomide. A few examples of questions to help you get started include:

  • Am I at a higher risk of side effects if I’m age 65 years or older?
  • Is my risk of hair loss higher when I first start treatment?
  • How do the side effects of leflunomide compare with those of other drugs used to treat rheumatoid arthritis, such as methotrexate?

To learn more about leflunomide or Arava, see these articles:

* A generic drug and its brand-name version are expected to have the same side effects because they contain the same active ingredient. (An active ingredient is what makes a drug work.)

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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.