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Hetlioz Side Effects

Generic Name: tasimelteon

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

For the Consumer

Applies to tasimelteon: oral capsule

Along with its needed effects, tasimelteon (the active ingredient contained in Hetlioz) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor as soon as possible if any of the following side effects occur while taking tasimelteon:

More Common

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

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

More Common

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.

Further information

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

Some side effects may not be reported. You may report them to the FDA.