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Generic name: tasimelteonTAS-i-MEL-tee-on ]
Brand names: Hetlioz, Hetlioz LQ
Drug class: Miscellaneous anxiolytics, sedatives and hypnotics

Medically reviewed by Judith Stewart, BPharm. Last updated on Jun 26, 2023.

What is Hetlioz?

Hetlioz 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 in adults.

Hetlioz is also used to treat nighttime sleep problems in people with a genetic disorder called Smith-Magenis Syndrome (SMS). The capsule form of Hetlioz is for people with SMS who are at least 16 years old. The oral suspension (liquid) form is for children with SMS who are from 3 to 15 years old.


After taking Hetlioz you should start preparing for bed. Tasimelteon can impair mental activities and alertness.

Use only as directed. Tell your doctor if you use other medicines or have other medical conditions or allergies.

Before taking this medicine

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

Tell your doctor if you are pregnant or breastfeeding.

Do not give this medicine to a child without medical advice. Hetlioz is approved to treat nighttime sleep problems only in children who have SMS and are at least 3 years old. Hetlioz is not approved to treat non-24-hour sleep-wake disorder in anyone younger than 18 years old.

How should I take Hetlioz?

Take Hetlioz exactly as prescribed by your doctor. Follow all directions on your prescription label and read all medication guides or instruction sheets.

Take the medicine without food, 1 hour before your normal bedtime at the same time each night.

Read and follow all Instructions for Use. Ask your doctor or pharmacist if you need help. Do not allow a young child to use Hetlioz without help from an adult.

Swallow the capsule whole and do not crush, chew, break, or open it.

Hetlioz capsules are for use in people 16 years and older. The oral suspension is for use only in children 3 to 15 years old.

Shake the oral suspension for at least 30 seconds before you measure a dose. Use the supplied syringe or a dose-measuring device (not a kitchen spoon). Do not remove the syringe adapter from the bottle neck. Recap the bottle and refrigerate after each use.

The capsules and liquid are not equivalent. Avoid medication errors by using only the form your doctor prescribes.

Doses are based on weight in children. Your child's dose may change if the child gains or loses weight.

You may not fully benefit from this medicine for several weeks or months.

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

Store the liquid medicine in the refrigerator. Throw away any leftover liquid 5 weeks after opening the 48 mL bottle, or 8 weeks after opening the 158 mL bottle.

Dosing information

Usual Adult Dose for Non-24-Hour Sleep-Wake Disorder:

20 mg orally once per day

-Take before bedtime, at the same time every night.
-Take without food.

Use: Treatment of Non-24-Hour Sleep-Wake Disorder (Non-24)

Usual Adult Dose for SMS Sleep Disturbances:

20 mg orally once per day

-Take before bedtime, at the same time every night.
-Take without food.

Use: Treatment of SMS Sleep Disturbances in patients 16 years of age and older

Usual Pediatric Dose for SMS Sleep Disturbances:

20 mg orally once per day in patients weighing over 28 kg
0.7 mg/kg orally once per day in patients weighing 28 kg or less

-Take before bedtime, at the same time every night.
-Take without food.

Use: Treatment of SMS Sleep Disturbances in patients 3 to 15 years of age

What happens if I miss a dose?

Skip the dose if you cannot take it at the regular time on a given night.

Do not use two doses at one time.

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?

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

Hetlioz side effects

Get emergency medical help if you have 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:

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?

Using Hetlioz with other drugs that make you drowsy can worsen this effect. Ask your doctor before using opioid medication, a sleeping pill, a muscle relaxer, or medicine for anxiety or seizures.

Sometimes it is not safe to use certain medications at the same time. Some drugs can affect your blood levels of other drugs you take, which may increase side effects or make the medications less effective.

Other drugs may interact with tasimelteon, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all other medicines you use.

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.