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Tasimelteon is used to treat non-24-hour sleep-wake disorder and nighttime sleep problems in people with Smith-Magenis Syndrome (SMS). Tasimelteon may work by helping to regulate the body’s circadian rhythm. Common side effects may include headache, nightmares or unusual dreams, and infection of the nose, throat, or bladder. Once you take your dose of tasimelteon, limit your activity to just preparing for bed. The medicine can affect your alertness or coordination.

Uses

What is tasimelteon used for?

Tasimelteon is commonly used to treat non-24-hour sleep-wake disorder (non-24), a condition in which a person’s internal clock that controls the sleep-wake cycle (circadian rhythm) does not match up with the 24-hour day. 

Tasimelteon may also be used to treat nighttime sleep problems in people who have Smith-Magenis Syndrome (SMS), a developmental disorder that can impact sleep and other behaviors. 

These uses may vary depending on the specific tasimelteon product prescribed. Tasimelteon may also be used for other conditions as determined by your health care provider.

How does tasimelteon work (mechanism of action)?

Tasimelteon binds to certain receptors that normally bind to melatonin, a hormone your brain makes naturally that helps with sleep. By acting on these receptors, tasimelteon may help control the body’s circadian rhythm.

How is tasimelteon supplied (dosage forms)?

Brands and other names

  • Hetlioz
  • Hetlioz LQ

Dosage forms and strengths

  • 20 mg oral capsules
  • 4 mg/mL oral suspension

How should I store tasimelteon?

Oral Capsule. Tasimelteon capsules should be stored at room temperature, between 68 F and 77 F (20 C and 25 C). They can be exposed to temperatures between 59 F and 86 F (15 C and 30 C) for shorter periods of time, such as when transporting them. Store in a cool, dry place. Protect from light and moisture.

Oral Liquid. Tasimelteon liquid should be stored in the refrigerator, between 36 F and 46 F (2 C and 8 C). After opening, throw away the 48 milliliter (mL) bottle after five weeks or the 158 mL bottle after eight weeks.

Side Effects

What are the most common side effects of tasimelteon?

The most common side effects of tasimelteon are listed below. Tell your health care provider if you have any of these side effects that bother you.

  • Headache
  • Increase in an enzyme mainly found in your liver called alanine aminotransferase
  • Nightmares or unusual dreams
  • Infection in the nose or throat, sore throat, or common cold symptoms
  • Kidney or bladder infection

There may be other side effects of tasimelteon that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088 (800-332-1088). In Canada, you can report side effects to Health Canada at www.canada.ca/en/health-canada/services/drugs-health-products/medeffect-canada or by calling 866-234-2345.

What are the serious side effects of tasimelteon?

While less common, the most serious side effects of tasimelteon are described below, along with what to do if they happen.

Severe Allergic Reactions. Tasimelteon may cause allergic reactions, which can be serious. Stop taking tasimelteon and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Warnings & Precautions

Who should not use tasimelteon?

Allergies to Ingredients. People who are allergic to any of the following should not take tasimelteon.

  • Hetlioz
  • Tasimelteon
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific tasimelteon products they stock.

What should I know about tasimelteon before using it?

Do not take tasimelteon unless it has been prescribed to you by a health care provider. Take it as prescribed.

Do not share tasimelteon with other people, even if they have the same condition as you. It may harm them.

Keep tasimelteon out of the reach of children. Since some forms of this medicine should be kept in a refrigerator, take special precautions to keep it away from children who also use the refrigerator.

There are multiple forms of tasimelteon available. Read and follow the instructions for the product you have and make sure you understand how to use it properly. If you have any questions, talk to your health care provider.

Swallow tasimelteon capsules whole. Do not open, crush, or chew tasimelteon capsules.

Shake the bottle of tasimelteon liquid for at least 30 seconds before drawing up each dose. Use the oral syringe that comes with the medicine to measure your dose. A household spoon is not an accurate measuring device and may cause you to take the wrong dose. Ask your pharmacist if you have any questions.

On the bottle of liquid tasimelteon, write the date that you first open the bottle. Once opened, the 48 milliliter (mL) bottle is only good for five weeks and the 158 mL bottle is only good for eight weeks. Throw away the bottle after these dates, even if you have medicine left over.

Tasimelteon can make you sleepy. Once you take your dose of tasimelteon, limit your activity to just preparing for bed. Since this medicine can affect your alertness or coordination, do not drive or do other activities that require alertness or coordination. 

People who are 65 or older can be at greater risk of some side effects from tasimelteon. Talk to your health care provider about your risks if you are in this age group.

It may take several weeks or months for tasimelteon to work, since each person’s circadian rhythm is different. You need to take it every night at the same time to get the most benefit from the medicine. Consider using an alarm or app to help you remember to take your dose every night.

What should I tell my health care provider before using tasimelteon?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if tasimelteon is right for you.

In particular, make sure that you discuss any of the following.

Smoking. Tell your health care provider if you smoke, start smoking, or quit smoking while taking tasimelteon. Smoking can make the medicine not work as well. 

Current and Past Health Conditions. Tell your health care provider about any health conditions you have or have had, such as liver problems.

Other Medicines and Supplements. Tasimelteon may interact with other medicines and supplements. Before taking tasimelteon, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. It is not known if or how tasimelteon could affect pregnancy or harm a fetus. Tell your health care provider if you are pregnant or plan to become pregnant.

Breastfeeding. It is not known if tasimelteon passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed. Your health care provider will let you know if you should take tasimelteon while breastfeeding.

Interactions

Does tasimelteon interact with foods or drinks?

Do not take tasimelteon with food. Taking it with food can make the medicine not work as well or as quickly. 

It is unknown if drinking alcohol will affect tasimelteon. The risk of sleepiness or problems with coordination and alertness may increase if you drink alcohol while taking tasimelteon.

Does tasimelteon interact with other medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before taking tasimelteon.

  • Fluvoxamine (Luvox), which is a medicine commonly used for obsessive-compulsive disorder (OCD)
  • Rifampin (Rifadin), which is a medicine commonly used to treat an infection called tuberculosis
  • Ketoconazole, which is a medicine used for fungal infections
  • A beta-blocker, such as atenolol (Tenormin), metoprolol (Lopressor, Toprol XL, and others), or propranolol (Inderal LA, Innopran XL), which is a medicine that may be used for certain heart conditions or to lower blood pressure

Many other medicines may alter the blood levels of tasimelteon. Tell your health care provider about all medicines that you take or have recently taken.

This may not be a complete list of medicines that can interact with tasimelteon. Always check with your health care provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much tasimelteon?

If you or someone else has used too much tasimelteon, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of tasimelteon?

Tasimelteon should be taken every night at the same time. If you cannot take the medicine at the same time on a given night, skip that dose and take the next dose as scheduled. Do not take double or extra doses.