Horizant (Gabapentin Enacarbil) - Oral

What Is Horizant?

Horizant (gabapentin enacarbil) is an oral prescription medication used to treat restless leg syndrome and nerve pain that can occur after having shingles. Horizant belongs to a group of drugs called anticonvulsants. It works to relieve shingles-related discomfort by altering how your body senses pain. Researchers don’t know for sure how Horizant works to treat restless leg syndrome.

Drug Facts

Generic Name: Gabapentin enacarbil

Brand Name(s): Horizant

Drug Availability: Prescription

Therapeutic Classification: Anticonvulsant

Available Generically: No

Controlled Substance: N/A

Administration Route: Oral

Active Ingredient: Gabapentin enacarbil

Dosage Form(s): Extended-release tablet

What Is Horizant Used For?

The Food & Drug Administration (FDA) has approved Horizant for the following uses:

Restless leg syndrome (RLS) is a condition that causes a strong urge to move your legs. Symptoms may feel worse when you are lying down or sitting still. You may feel a creeping, tingling, or burning sensation in your legs. RLS can impact your ability to fall or stay asleep. Horizant can help calm these uncomfortable symptoms.

Postherpetic neuralgia describes the severe pain that can occur after a case of shingles (herpes zoster). The pain occurs in the area where you had the shingles rash. Postherpetic neuralgia can last for months and even years in some people. The pain may make it difficult to sleep or concentrate throughout the day. Horizant offers relief from this painful shingles complication.

How to Take Horizant

If you’re taking Horizant to treat symptoms of restless leg syndrome, your healthcare provider will likely tell you to take Horizant once daily at 5 pm. For postherpetic neuralgia, Horizant is typically taken twice per day. Horizant is an extended-release tablet, so it’s important to swallow the tablet whole without cutting, crushing, or chewing. 

Horizant should be taken with food to help your body absorb the medication. Be sure to avoid alcohol since combining alcohol with Horizant can increase your risk of side effects. 

Don’t stop taking Horizant without speaking to your healthcare provider first. Stopping Horizant all of a sudden can cause side effects, so your healthcare provider may slowly decrease your dose if you no longer need treatment.

Storage

Horizant should be stored at room temperature, away from moisture.

Keep your medications tightly closed and out of the reach of children and pets, ideally locked in a cabinet or closet.

Avoid pouring unused and expired drugs down the drain or in the toilet. Ask your pharmacist or healthcare provider about the best ways to dispose of this medicine. Visit the FDA's website to know where and how to discard all unused and expired drugs. You can also find disposal boxes in your area. Ask your pharmacist or healthcare provider if you have any questions about the best ways to dispose of your medications.

If you travel with Horizant, get familiar with your final destination's regulations. In general, be sure to make a copy of your Horizant prescription. Keep your medication in its original container from your pharmacy with your name on the label. Ask your pharmacist or healthcare provider if you have any questions about traveling with your medicine.

How Long Does Horizant Take to Work?

Horizant begins to improve symptoms of restless leg syndrome as early as two days after starting treatment. If you’re using Horizant to treat the pain of postherpetic neuralgia, you’ll likely notice improvements within the first week.

Off-Label Uses

Gabapentin has been used off-label for attention deficit disorder, bipolar disorder, complex regional pain syndrome, diabetic neuropathy, drug and alcohol withdrawal seizures, migraine, neuropathic pain, periodic limb movement disorder of sleep, restless leg syndrome, and trigeminal neuralgia. However, most of this data pertains to gabapentin immediate release (neurontin), not the enacarbil salt (Horizant).

What Are the Side Effects of Horizant?

This is not a complete list of side effects, and others may occur. A healthcare provider can advise you on side effects. If you experience other effects, contact your pharmacist or a healthcare provider. You may report side effects to the Food and Drug Administration (FDA) at fda.gov/medwatch or 800-FDA-1088.

Common Side Effects

You may experience side effects while taking Horizant. Be sure to let your healthcare provider know if you develop any side effects that bother you or don’t go away. 

Common side effects include:

  • Dizziness 
  • Headache 
  • Sleepiness

Dizziness and sleepiness typically go away several weeks after starting Horizant. It’s important not to drive until you know how Horizant affects you.

Severe Side Effects

Rarely, Horizant may cause serious side effects. Call your healthcare provider right away if you develop any severe reactions. Call 911 if your symptoms feel life-threatening or if you think you’re having a medical emergency.

Serious side effects and their symptoms include:

  • Impaired ability to drive a car: Horizant can cause sleepiness, dizziness, slow thinking, and affect your coordination, even the morning after you take your dose. Do not drive or perform any other dangerous activity until you know how Horizant will affect you. 
  • Mood or behavior changes: Horizant may rarely cause suicidal thoughts or actions. Monitor for any changes in your mood, including new or worsening depression, anxiety, agitation, aggression, or trouble sleeping. Report any changes in your mood or behavior to your healthcare provider right away. 
  • Serious breathing problems: Horizant can slow your breathing, especially if you take it with other medicines that make you feel sleepy or if you already have breathing problems. Contact your healthcare provider right away if you develop any trouble breathing.

Horizant may also cause a severe allergic reaction involving the skin, liver, blood cells, or other body parts. You may not always have a rash. Call your healthcare provider right away if you notice any of the following:

  • Fever
  • Frequent infections 
  • Rash or hives 
  • Severe tiredness or weakness 
  • Severe muscle pain 
  • Swelling of your lips or tongue
  • Swollen glands that do not go away
  • Unusual bruising or bleeding 
  • Yellowing of your skin or the white parts of your eyes

Report Side Effects

Horizant may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your healthcare provider may send a report to the FDA's MedWatch Adverse Event Reporting Program or by phone (800-332-1088).

Dosage: How Much Horizant Should I Take?

Drug Content Provided and Reviewed by IBM Micromedex®

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For oral dosage form (extended-release tablets):
    • For restless legs syndrome:
      • Adults—600 milligrams (mg) as a single dose at about 5 PM. Your doctor may adjust your dose as needed and tolerated.
      • Children—Use and dose must be determined by your doctor.
    • For postherpetic neuralgia:
      • Adults—At first, 600 milligrams (mg) once a day taken in the morning for 3 days. Then, your doctor will increase your dose to 600 mg two times a day. Your doctor may adjust your dose as needed and tolerated. However, the dose is usually not more than 1,200 mg per day.
      • Children—Use and dose must be determined by your doctor.

Modifications

The following modifications (changes) should be kept in mind when using Horizant:

Severe allergic reaction: Avoid using Horizant if you have a known allergy to it or its ingredients. Ask your pharmacist or healthcare provider for a complete list of the ingredients if you're unsure.

Pregnancy: There's not enough information about the safety and effectiveness of Horizant in pregnant people and their unborn fetuses. Discuss with your healthcare provider if you plan to become pregnant or are pregnant, and weigh the benefits and risks of taking Horizant during your pregnancy.

Breastfeeding: There's not enough information about the safety of Horizant in human breastmilk and nursing babies. Talk with your healthcare provider if you plan to breastfeed, weigh the benefits and risks of taking Horizant while nursing, and the different ways available to feed your baby.

Adults over 65: Clinical studies haven't included a large enough number of people in this age group to see whether they respond differently from younger adults. Older adults with several medical conditions or taking several medications should use caution with Horizant. Some older adults might also be more sensitive to Horizant side effects.

Children: It's unknown whether Horizant is safe or effective in children. 

Kidney problems: Individuals with kidney problems may not be able to clear medication from their bodies as easily. This means the medicine stays in the body longer and can have increased side effects. For this reason, your healthcare provider will likely not prescribe Horizant beyond a certain dosage if you have severe kidney impairment.

Missed Dose

If you accidentally forgot your Horizant dose, take it as soon as you remember. If it's already close to your next scheduled dose, skip the missed dose and take the following dose at your next scheduled dosing time. Don't try to double up to make up for the missed dose.

Try to find ways that work for you to help yourself remember to keep your appointments and take your medication routinely. If you miss too many doses, Horizant might be less effective at treating your condition.

Overdose: What Happens If I Take Too Much Horizant?

Taking too much Horizant can be dangerous. Deaths have occurred following Horizant overdoses, so it’s important that you only take your prescribed dose. Symptoms of an overdose include double vision, tremors (shaking), slurred speech, drowsiness, confusion, dizziness, fatigue, and diarrhea. 

If you think you or someone else may have overdosed on Horizant, call your healthcare provider or the Poison Control Center. If your symptoms feel life-threatening, call 911.

What Happens If I Overdose on Horizant?

If you think you or someone else may have overdosed on Horizant, call a healthcare provider or the Poison Control Center (800-222-1222).

If someone collapses or isn't breathing after taking Horizant, call 911 immediately.

Precautions

Drug Content Provided and Reviewed by IBM Micromedex®

It is very important that your doctor check your progress at regular visits. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to take it.

Gabapentin enacarbil may cause dizziness, drowsiness, or sleepiness. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are not alert. If these side effects are especially bothersome, check with your doctor.

This medicine may cause some people to be agitated, irritable, or display other abnormal behaviors, such as feeling sad or hopeless, getting upset easily, or feeling nervous, restless, or hostile. It may also cause some people to have suicidal thoughts and tendencies or to become more depressed. If you or your caregiver notice any of these side effects, tell your doctor right away.

This medicine may cause respiratory depression, a serious breathing problem that can be life-threatening, when used together with narcotic pain medicines. Check with your doctor right away if you have pale or blue lips, fingernails, or skin, difficult or troubled breathing, or irregular, fast or slow, or shallow breathing.

Check with your doctor right away if you have a fever, rash, swollen, painful, or tender lymph glands in the neck, armpit, or groin, unusual bleeding or bruising, or yellow eyes or skin. These may be symptoms of a serious and life-threatening allergic reaction called drug reaction with eosinophilia and systemic symptoms (DRESS) or multiorgan hypersensitivity.

Do not stop using this medicine without checking with your doctor. Stopping the medicine suddenly may cause seizures. Your doctor may want you to gradually reduce the amount you are taking before stopping it completely.

Do not drink alcohol while you are using this medicine.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

What Are Reasons I Shouldn’t Take Horizant?

If you're allergic to Horizant or any of its ingredients, avoid using it. Ask your pharmacist or healthcare provider for a complete list of the ingredients if you're unsure.

Certain conditions may increase your risk of developing complications from Horizant. Let your healthcare provider know about all your medical conditions and allergies so they can determine if Horizant is the best treatment for you. 

Horizant contains a form of gabapentin. Be sure to let your healthcare provider know if you’ve ever had an allergic reaction to any product containing gabapentin (e.g., Gralise, Neurontin). 

You should not take Horizant for restless leg syndrome if you need to sleep during the daytime and stay awake at night. Let your healthcare provider know if your work schedule requires you to change your sleep patterns frequently.

What Other Medications Interact With Horizant?

Many medications may interact with Horizant. Let your healthcare provider know about all your medicines, including over-the-counter (OTC) and nonprescription products. 

Any medication or substance that makes you sleepy can increase your chance of developing side effects with Horizant. This includes alcohol. Alcohol also increases how quickly Horizant is absorbed into your body, adding to the sedative effects. 

Watch out for any other medicines that make you feel tired. Sedating medicines include:

Let your healthcare provider know if you take any other medications that contain gabapentin (e.g., Gralise, Neurontin). It would help if you did not take these medicines with Horizant. 

This is not a complete list of all the drugs that may interact with Horizant. Always keep an up-to-date list of your medicines, and let your healthcare provider and pharmacist know any time there are changes.

What Medications Are Similar?

Horizant is an anticonvulsant medicine that contains a long-acting form of gabapentin (gabapentin enacarbil). Other similar medications include:

  • Neurontin (gabapentin)
  • Gralise (gabapentin, extended-release)
  • Lyrica (pregabalin) 
  • Lyrica CR (pregabalin, extended-release)

The above medications are also approved to treat postherpetic neuralgia but not restless leg syndrome (RLS). However, some healthcare providers may prescribe these medicines “off-label” for RLS. 

Horizant has the advantage of only needing to be dosed once per day.  Gralise and Lyrica CR are also taken once daily, but Neurontin and Lyrica require several doses per day to be effective. Long-acting products generally are more expensive than their short-acting counterpart. You and your healthcare provider will work together to find a treatment option that considers cost and your prescription medication coverage. 

This list is a list of drugs also used to treat postherpetic neuralgia and RLS. It is NOT a list of drugs recommended to take with Horizant. You should not take these drugs together. Instead, ask your pharmacist or a healthcare provider if you have questions.

Frequently Asked Questions

  • What is Horizant used for?

    Horizant is used to treat the uncomfortable symptoms of restless leg syndrome (e.g., strong urge to move your legs, tingling, creeping, burning). Horizant also helps relieve the pain that can occur after having shingles—a complication called postherpetic neuralgia.

  • How does Horizant work?

    Horizant helps treat postherpetic neuralgia by affecting how your body senses pain. Researchers don’t know for sure how Horizant works for treating restless leg syndrome.

  • What drugs should not be taken with Horizant?

    Any medicine or substance that makes you sleepy should not be taken with Horizant since it can increase your risk of developing side effects. You should also avoid alcohol while taking Horizant.

How Can I Stay Healthy While Taking Horizant?

If you’re struggling with postherpetic neuralgia or restless leg syndrome symptoms, your healthcare provider may prescribe Horizant to help you get some relief. Because Horizant can make you feel tired and dizzy, your ability to drive a car may be significantly impaired. Therefore, it’s important not to drive or do any other dangerous activity until you know how Horizant affects you. If you’re already taking medicines that make you sleepy, the side effects of Horizant can be worse. Let your healthcare provider know about all the medicines you take to determine if Horizant is a safe treatment option for you.

Medical Disclaimer

Verywell Health's drug information is meant for educational purposes only and is not intended as a replacement for medical advice, diagnosis, or treatment from a healthcare provider. Consult your healthcare provider before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Christina Varvatsis, PharmD
Christina Varvatsis is a hospital pharmacist and freelance medical writer. She is passionate about helping individuals make informed healthcare choices by understanding the benefits and risks of their treatment options.