If you or a loved one has Lennox-Gastaut syndrome (LGS), you may want to learn more about Onfi (clobazam), which treats seizures related to this condition. (LGS is a severe form of epilepsy that starts in childhood.)

Onfi is a prescription drug used to treat seizures from LGS in adults and in children ages 2 years and older. Onfi is prescribed along with other seizure drugs.

Onfi is available as a tablet or as a suspension (a type of liquid mixture). You take both forms by mouth. If Onfi works well for you, you’ll likely take it long term.

For more information about Onfi, including details about its use for LGS-related seizures, see this in-depth article.

Keep reading to learn more about the main side effects of Onfi.

Like most drugs, Onfi may cause mild or serious side effects in some people. But some side effects are more common than others.

Commonly reported side effects of Onfi include:

See below for other side effects Onfi may cause.

* To learn more about this side effect, see “Side effects explained” below.
† To learn more about these side effects, see “Mood changes, thoughts of suicide, or suicidal behaviors” under “Side effects explained” below.

Below is a list of mild side effects that Onfi may cause. In most cases, these side effects should be manageable. Or they may ease with continued use of the drug.

If any side effects seem serious, get worse, or don’t improve, talk with your doctor or pharmacist. But do not stop using Onfi unless your doctor recommends it.

Examples of mild side effects that have been reported with Onfi include:

* To learn more about this side effect, see “Side effects explained” below.
† To learn more about these side effects, see “Mood changes, thoughts of suicide, or suicidal behaviors” under “Side effects explained” below.

Onfi may cause mild side effects other than the ones listed above. See the Onfi medication guide for details.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with Onfi, visit MedWatch.

Onfi may cause serious side effects, but this is uncommon. Serious side effects that have been reported with Onfi include:

If you experience serious side effects with Onfi, call your doctor right away. If the symptoms seem life threatening or if you think you’re having a medical emergency, call 911 or your local emergency number right away.

Some people may have a higher risk for certain serious side effects. If you’re concerned about your risk for serious side effects, talk with your doctor.

* Onfi 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 the “Side effects explained” section below.
** Onfi has a boxed warning for this side effect. To learn more, see the “Onfi and misuse” section below.
† To learn more about this side effect, see “Side effects explained” below.
‡ An allergic reaction is possible after using Onfi. But this side effect wasn’t reported in studies.

See below for answers to some frequently asked questions about Onfi’s side effects.

Are there any possible long-term side effects from taking Onfi?

It’s not likely that you’ll have long-term side effects from Onfi.

Some side effects that you experience when you first start treatment may go away after you’ve used the drug for a while. For example, drowsiness may improve with time. However, some people may still experience side effects after using Onfi long term.

If you’re concerned about long-term side effects with Onfi, talk with your doctor.

Can Onfi cause side effects in toddlers? If so, which ones?

Yes, Onfi can cause side effects in toddlers.

Onfi is used to treat seizures caused by Lennox-Gastaut syndrome (LGS) in adults and in certain children. This includes toddlers ages 2 years and older with LGS. Onfi’s safety and effectiveness in toddlers younger than 2 years of age is unknown, and it’s not approved for children in this age group.

In toddlers ages 2 years and older, the possible side effects with Onfi are the same as those seen in adults. See the sections above to learn about the common, mild, and serious side effects of Onfi, or refer to the Onfi medication guide.

If you have questions about your child’s risk for side effects with this drug, talk with their doctor or your pharmacist.

Does the generic version of Onfi cause the same side effects as the brand-name drug?

Yes, Onfi and its generic version (clobazam) can cause the same side effects. A generic drug is an exact copy of the active drug in a brand-name medication. This means the drugs have the same effects in your body, including side effects.

If you’re interested in learning more about the generic version of Onfi, talk with your doctor or pharmacist.

I’m starting Onfi treatment with a 10-mg dose. Do any of the drug’s side effects vary depending on dose?

Yes, some of Onfi’s side effects may be related to dose.

For example, drowsiness is a dose-related side effect of Onfi. You may feel drowsier if you take higher doses of the drug. But this side effect may be reduced after you’ve taken the drug for a while.

Onfi belongs to a group of drugs called benzodiazepines. Typically, these drugs have stronger side effects as the dose increases. Examples of these effects include fatigue (lack of energy) and extreme tiredness. These are both side effects of Onfi, so you may experience more fatigue or tiredness with higher doses of the drug.

If you’re concerned about dose-related side effects with Onfi, talk with your doctor or pharmacist.

Does Onfi cause any cognitive side effects?

It’s possible that you may experience cognitive side effects with Onfi, such as slowed thinking.

Like other seizure drugs, Onfi is a central nervous system depressant. These drugs can cause cognitive side effects.

Cognitive side effects occur when a drug affects your brain’s ability to process information or function normally. You may notice changes in your:

  • mental alertness or clarity
  • ability to problem solve or make decisions
  • memory or ability to concentrate

Older seizure drugs, such as phenobarbital and Dilantin (phenytoin), may cause more cognitive side effects than newer drugs such as Onfi. But Onfi may be used with certain older drugs to treat seizures in people with Lennox-Gastaut syndrome.

If you’re concerned about experiencing cognitive side effects with Onfi, talk with your doctor.

Read on to learn more about some of the side effects Onfi may cause.

Boxed warnings

Onfi has two boxed warnings related to side effects. Boxed warnings are the most serious warnings from the Food and Drug Administration (FDA). They alert doctors and patients about drug effects that may be dangerous.

Risk of dependence and withdrawal

While taking Onfi, your body may begin relying on the drug in order to feel normal. This is called dependence. Because of the risk of dependence, stopping Onfi suddenly can lead to serious or life threatening withdrawal symptoms.

Examples of possible symptoms include:

Although dependence and withdrawal weren’t seen in studies of Onfi, they can still occur. If you have questions about your risk for dependence and withdrawal, talk with your doctor or pharmacist.

Risk of severe side effects when taken with opioids

Taking Onfi with opioids (drugs prescribed for severe pain) raises your risk for severe side effects, including:

Examples of opioid medications include oxycodone/acetaminophen (Percocet) and morphine (Kadian, MS Contin).

What might help

If your doctor determines you should stop taking Onfi, they’ll lower your dosage slowly over time. Doing so lowers the risk of withdrawal symptoms.

Before starting Onfi, talk with your doctor about any medications you currently use. And before starting any new medication for pain or cough, tell the prescribing doctor that you take Onfi. If your doctor still wants to prescribe an opioid medication, they’ll also discuss the risks of using it with Onfi. And they may lower your Onfi dosage to reduce any risk of severe side effects.

Vomiting

Taking Onfi may cause vomiting in some people. In a study of Onfi, vomiting was a common side effect.

What might help

If you experience mild vomiting with Onfi, take steps to avoid dehydration (loss of too much body fluid). But before using over-the-counter electrolyte solutions to rehydrate, talk with your doctor. They can advise you on the best way to replace lost body fluids.

Keep in mind that mild vomiting should go away once your body becomes used to Onfi. But if your vomiting continues or becomes more severe, see your doctor right away. They’ll make sure you have enough fluids, and they may prescribe medication to help stop the vomiting.

Upper respiratory infections

While using Onfi, you may have a higher risk for upper respiratory infection such as the common cold. Upper respiratory infections were a common side effect in a study of Onfi.

What might help

The following tips may help prevent upper respiratory infections during your Onfi treatment.

  • Wash your hands regularly with soap and water, or use hand sanitizer.
  • Stay up to date on vaccines, as recommended by your doctor.
  • During cold and flu season, avoid crowds when possible.
  • Wait until sick friends or family are better before seeing them.

If you have an infection with symptoms that don’t go away or seem severe, see your doctor right away. Some upper respiratory infections are caused by bacteria. Your doctor may prescribe an antibiotic to treat the infection. Or they may suggest treatment to help with a cough or trouble breathing. This may include an over-the-counter drug to break up mucus or a prescription drug to help open your airways.

If you have concerns about getting upper respiratory infections with Onfi, talk with your doctor.

Mood changes, thoughts of suicide, or suicidal behaviors

Like all seizure drugs, Onfi may cause new or worsening mood problems (such as depression), thoughts of suicide, or suicidal behaviors.

It’s unclear how often these effects have happened with Onfi. They weren’t specifically reported in studies of Onfi. But in one study, aggression and irritability were commonly reported side effects of the drug. And these side effects can be symptoms of mood changes or depression.

What might help

During your Onfi treatment, tell your doctor right away if you experience any new or worsening symptoms of depression or other mood changes, unusual behaviors, thoughts of self-harm, or suicidal actions. Ask your friends and family to watch for any changes in your mood or behavior, too.

If you have questions or concerns about your risk for these side effects, talk with your doctor.

SUICIDE PREVENTION

If you think someone is at immediate risk of self-harm or hurting another person:

  • Call 911 or your local emergency number.
  • Stay with the person until help arrives.
  • Remove any guns, knives, medications, or other things that may cause harm.
  • Listen, but don’t judge, argue, threaten, or yell.

If you or someone you know is considering suicide, get help from a crisis or suicide prevention hotline. Try the National Suicide Prevention Lifeline at 800-273-8255.

Allergic reaction

Like most drugs, Onfi can cause an allergic reaction in some people. But this side effect wasn’t reported in studies.

Symptoms can be mild or serious and can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)
  • 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 might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest an over-the-counter oral antihistamine, such as Benadryl (diphenhydramine), or a topical product, such as hydrocortisone cream, to manage your symptoms.

If your doctor confirms it’s a mild allergic reaction to Onfi, they’ll decide if you should continue using it.

For 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 had a serious allergic reaction to Onfi, they may have you stop taking Onfi and switch to a different treatment.

Keeping track of side effects

During your Onfi treatment, consider keeping notes on any side effects you’re having. Then, you can share this information with your doctor. This is especially helpful to do when you first start taking new drugs or using a combination of treatments.

Your side effect notes can include things such as:

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

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

Onfi has several warnings that may affect you or your loved one’s ability to safely use this drug. See below.

Boxed warnings

Onfi has the following boxed warnings. Boxed warnings are the most serious warnings from the Food and Drug Administration (FDA).

  • Risk of misuse and addiction. Using Onfi raises the risk for misuse and addiction. Misusing Onfi means taking it in a different way than it was prescribed. Addiction means using Onfi even though it’s causing harm. To learn more, see the “Onfi and misuse” section below.
  • Risk of dependence and withdrawal. While taking Onfi, your body may begin relying on the drug in order to feel normal. This is called dependence. Because of the risk of dependence, stopping Onfi suddenly can lead to serious or life threatening withdrawal symptoms. To learn more, see the “Side effects explained” section above.
  • Risk of severe side effects when taken with opioids. People who take Onfi with opioids are at risk for severe side effects. These may include extreme sedation (state of deep sleep), respiratory depression (weak or slow breathing), coma, and in rare cases, even death. To learn more, see the “Side effects explained” section above.

Other warnings

Onfi may not be the right option if you have certain medical conditions or other factors that affect your health. Talk with your doctor about your health history before taking Onfi. The list below includes factors to consider.

Mood changes, thoughts of suicide, or suicidal behaviors. Like all seizure drugs, Onfi may cause new or worsening mood problems (such as depression), thoughts of suicide, or suicidal behaviors. If you have any mental health conditions or have had them before, tell your doctor before taking Onfi. During your treatment, tell your doctor right away if you experience any new or worsening symptoms of depression or other mood changes, unusual behaviors, thoughts of self-harm, or suicidal actions. Ask your friends and family to watch for any changes in your mood or behavior, too.

Serious kidney problems. It’s unclear if Onfi is safe to use in people with serious kidney problems. Before taking Onfi, talk with your doctor about your kidney health. They’ll determine if Onfi is a safe option for you.

Liver disease. Onfi is broken down by your liver. If you have liver problems, your body might not be able to break down and get rid of the drug. This could cause Onfi levels to build up in your body. Before using Onfi, talk with your doctor about your liver health. If needed, they may prescribe a lower dosage of Onfi for you.

Allergic reaction. If you’ve had an allergic reaction to Onfi or any of its ingredients, you should not take Onfi. Ask your doctor what other medications are better options for you.

Alcohol use and Onfi

It’s not safe to drink alcohol while taking Onfi. Alcohol and Onfi can both suppress your central nervous system. This means they can slow your brain activity. Using alcohol and Onfi together raises your risk for dangerous side effects, such as extreme drowsiness, slowed thinking, and lack of coordination.

Plus, drinking alcohol with Onfi can increase the level of the drug in your body. This raises your risk for side effects, some of which may be serious.

If you drink alcohol and have concerns about not drinking during your Onfi treatment, talk with your doctor.

Pregnancy and breastfeeding while taking Onfi

Taking Onfi while pregnant or breastfeeding may be unsafe.

If you’re pregnant or breastfeeding or planning to become pregnant or to breastfeed, talk with your doctor before using Onfi. They can determine whether Onfi is right for you.

If you do use Onfi during pregnancy, consider signing up for the North American Antiepileptic Drug Pregnancy Registry. This program helps collect data on the safety of using seizure drugs during pregnancy. You can learn more by visiting the program website.

Onfi has a boxed warning for the risk of misuse and addiction. Boxed warnings are the most serious warnings from the Food and Drug Administration (FDA). They alert doctors and patients about drug effects that may be dangerous.

Misusing Onfi means taking it in a different way than it was prescribed. Addiction means using Onfi even though it’s causing harm.

Misusing Onfi is dangerous and can lead to overdose or death. It’s important to note that misuse and addiction were not seen in studies of Onfi. But they have been seen with other benzodiazepines. (Onfi is a benzodiazepine.)

Anyone who has misused or had an addiction to illegal drugs or prescription medications, or has had an addiction to alcohol, should talk with their doctor before taking Onfi. Their doctor can determine if Onfi is the right drug.

Onfi can be an effective treatment for seizures related to Lennox-Gastaut syndrome. This drug may cause side effects in some people. But most side effects are mild, and serious side effects aren’t common.

To learn more about Onfi’s side effects, talk with your doctor or pharmacist. Get answers to your questions to feel confident about your treatment plan. Questions you may want to ask include:

  • If my child has cognitive side effects with Onfi, will these side effects ease with time?
  • Why does drinking alcohol increase the amount of Onfi in my body? Does this happen even if I only drink once in a while?
  • If my child develops drooling with Onfi, is there anything I can do to treat this?

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.