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Generic Name: tasimelteon (TAS i MEL tee on)
Brand Names: Hetlioz

Medically reviewed by Last updated on Mar 4, 2019.

What is Hetlioz?

Hetlioz (tasimelteon) is a sedative, also called a hypnotic. It works by affecting certain substances in your body that help regulate your "sleep-wake cycle."

Hetlioz is used to treat non-24-hour sleep-wake disorder.

Hetlioz may also be used for purposes not listed in this medication guide.

Important information

Follow all directions on your medicine label and package. Tell each of your healthcare providers about all your medical conditions, allergies, and all medicines you use.

Before taking this medicine

You should not use Hetlioz if you are allergic to tasimelteon.

To make sure Hetlioz is safe for you, tell your doctor if you have:

  • liver disease; or

  • if you smoke.

FDA pregnancy category C. It is not known whether Hetlioz will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant while using this medicine.

It is not known whether tasimelteon passes into breast milk or if it could harm a nursing baby. Tell your doctor if you are breast-feeding a baby.

How should I take Hetlioz?

Take Hetlioz exactly as your health care provider tells you. Follow all directions on your prescription label. Do not take this medicine in larger or smaller amounts or for longer than recommended.

Take the medicine before your normal bedtime, at the same time each night.

Do not crush, chew, break, or open a Hetlioz capsule. Swallow it whole.

For best results, take Hetlioz without food.

After you take Hetlioz, avoid doing anything other than getting ready for bed.

It may take several weeks or months before your symptoms improve. Keep using the medication as directed and tell your doctor if your symptoms do not improve.

Store at room temperature away from moisture, heat, and light.

What happens if I miss a dose?

Since Hetlioz is usually taken as needed, you may not be on a dosing schedule. Hetlioz should be taken only at your normal bedtime. Do not take extra medicine to make up a missed dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What should I avoid while taking Hetlioz?

This medicine may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert.

Drinking alcohol may increase drowsiness caused by Hetlioz.

Hetlioz side effects

Get emergency medical help if you have any of these signs of an allergic reaction to Hetlioz: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

  • pain or burning when you urinate.

Side effects may be more likely in older adults.

Common Hetlioz side effects may include:

  • drowsiness;

  • headache;

  • strange dreams, nightmares; or

  • cold symptoms such as stuffy nose, sneezing, sore throat.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What other drugs will affect Hetlioz?

Taking this medicine with other drugs that make you sleepy can worsen this effect. Ask your doctor before taking Hetlioz with another sleeping pill, narcotic pain medicine, muscle relaxer, or medicine for anxiety, depression, or seizures.

Tell your doctor about all medicines you use, and those you start or stop using during your treatment with Hetlioz, especially:

  • ciprofloxacin;

  • enzalutamide;

  • fluvoxamine;

  • mitotane;

  • rifampin;

  • St. John's wort; or

  • seizure medicine--carbamazepine, fosphenytoin, phenobarbital, or phenytoin.

This list is not complete. Other drugs may interact with tasimelteon, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed in this medication guide.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Hetlioz only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.