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Hetlioz Side Effects

Generic Name: tasimelteon

Note: This page contains information about the side effects of tasimelteon. Some of the dosage forms included on this document may not apply to the brand name Hetlioz.

For the Consumer

Applies to tasimelteon: oral capsule

In addition to its needed effects, some unwanted effects may be caused by tasimelteon (the active ingredient contained in Hetlioz). In the event that any of these side effects do occur, they may require medical attention.

Severity: Moderate

If any of the following side effects occur while taking tasimelteon, check with your doctor or nurse as soon as possible:

More common:
  • Bladder, lower back, or side pain
  • bloody or cloudy urine
  • difficult, burning, frequent, or painful urination

Minor Side Effects

Some of the side effects that can occur with tasimelteon may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

More common:
  • Body aches or pain
  • chills or fever
  • cough
  • ear congestion
  • headache
  • nasal congestion, runny nose, or sneezing
  • nightmares

For Healthcare Professionals

Applies to tasimelteon: oral capsule

Nervous system

Very common (10% or more): Headache (17%)
Frequency not reported: Somnolence[Ref]


Very common (10% or more): Increased ALT (10%)[Ref]


Very common (10% or more): Nightmare/abnormal dreams (10%)


Common (1% to 10%): Urinary tract infection[Ref]


Common (1% to 10%): Upper respiratory tract infection[Ref]


1. "Product Information. Hetlioz (tasimelteon)." Vanda Pharmaceuticals Inc, Rockville, MD.

Not all side effects for Hetlioz may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.