Tasimelteon (Oral)

As a selective agonist for the melatonin receptors (MT1 and MT2), Tasimelteon helps patients (particularly those who are blind or visually impaired) to experience better sleep timing regulation.


Tasimelteon is used to help regulate sleep pattern in patients suffering from non-24-hour sleep-wake disorder. It was initially developed as a research chemical designed to potentially treat a variety of different sleep disorders, with the drug being granted orphan status in 2008, followed by status as an investigational medication in 2010.

This medication has not been tested in minors or non-blind people, and is only FDA-approved for those with no eyesight. It is therefore only recommended for use by those who are registered clinically blind, and only for use as prescribed by a qualified physician.

It is thought that the drug may be beneficial in combating insomnia associated with shift work, jet lag and exposure to bright lights at night time, which can result in the desynchronization of the internal body clock.

In the US, UK and throughout the EU, Tasimelteon is often marketed by Vanda Pharmaceuticals as Hetlioz.

Conditions treated

  • Non-24-hour sleep-wake disorder

Type of Medicine

  • Melatonin agonist

Side effects

Along with the desired effects (regulation of the internal body clock, dissipation of insomnia and/or other sleep disorders), Tasimelteon also has the potential to cause many unwanted and potentially unpleasant side effects. The most common side effects reported by users undergoing treatment with this medication include: elevated liver enzymes in the blood, nightmares or abnormal dreams, headache, sleep disturbance, drowsiness, infections in the upper respiratory tract, and/or urinary tract infections.

As the patient continues his or her course of treatment as prescribed, the severity of the side effects they experience should lessen to the point where they are tolerable or no longer noticeable. Many patients experience no side effects at all when undergoing treatment with Tasimelteon, and some of the side effects are actually alleviated by the drug once the body adjusts to it. As such, the benefit of taking Tasimelteon is often outweighed by the potential to experience uncomfortable side effects.

If side effects persist for a prolonged period or become more intense as treatment continues, the patient is advised to notify their healthcare provider immediately. In many instances, a doctor or physician may be able to advise ways to alleviate particularly uncomfortable side effects, via another medicine or natural remedy, for example.


As with all prescribed medicines, it is incredibly important for patients to only take Tasimelteon as prescribed by their physician. This means that patients should avoid taking larger doses than advised. Additionally, patients should be of the understanding that they should cease using this medicine when advised to do so by a healthcare professional, even if they still have a supply of the drug remaining.

Tasimelteon is taken orally, in pill form. For the treatment of insomnia or other non-specific non-24-hour sleep disorders, the patient should take 20mg per day, before bedtime, at the same time every evening. Tasimelteon should be taken without food, at least two hours after eating but preferably longer. On the advice of a doctor, this dose may vary. If this is not the case, the instructions printed on the literature supplied with the medicine should be read closely and adhered to.

Safety and efficacy of this dosage has not been established in patients younger than 18 years of age. A doctor may elect to treat patients under the age of 18 with Tasimelteon, with a dose chosen at their discretion, based on the severity of the patient's symptoms, as well as the physiology of the patient.

If the standard dose of Tasimelteon cannot be administered at the usual time on a given evening, that evening's dose should be skipped, with the patient returning to the normal dosage cycle the following evening. Patients are advised against taking a double dose to make up for the missed dose, as this can result in potentially harmful effects (overdose). In the event of an overdose, the patient or their caregiver should contact their local poison control center or emergency department immediately.

Tasimelteon capsules should be swallowed whole, preferably with a glass of water. Patients are advised against chewing, breaking or crushing capsules, or dissolving them in water, as this could afect the efficacy of the dose.


All drugs have the potential to react with other medicines or chemicals within the human body. These interactions can potentially cause one or more medicines to become ineffective in treating a condition, and in certain cases some interactions can give rise to potentially harmful or even fatal side effects. Because of these dangers, patients are advised to keep a detailed and up-to-date list of all medications they are currently taking. This includes vitamins, herbal supplements and over the counter remedies as well as prescription medications. The more the patient's doctor knows about their current medical situation, the greater opportunity they will have to spot any potentially unwanted interactions.

Below is a list of drugs known to have interacted negatively with Tasimelteon. Patients who are currently undergoing treatment with one or more of these medicines should inform their doctor prior to beginning treatment with Tasimelteon:

  • Abilify (aripiprazole)
  • Abilify Discmelt (aripiprazole)
  • Abilify Maintena (aripiprazole)
  • Abilify MyCite (aripiprazole)
  • Abstral (fentanyl)
  • alprazolam
  • Alprazolam Intensol (alprazolam)
  • Altafed (pseudoephedrine / triprolidine)
  • Altarussin CF (dextromethorphan / guaifenesin / pseudoephedrine)
  • Agenerase (amprenavir)
  • Agrylin (anagrelide)
  • AH-Chew (chlorpheniramine / methscopolamine / phenylephrine)
  • atazanavir
  • atazanavir / cobicistat
  • Ativan (lorazepam)
  • Atridine (pseudoephedrine / triprolidine)
  • Atripla (efavirenz / emtricitabine / tenofovir)
  • Atrofed (pseudoephedrine / triprolidine)
  • Atrogen (pseudoephedrine / triprolidine)
  • Codegest Expectorant (codeine / guaifenesin / phenylpropanolamine)
  • Codehist DH (chlorpheniramine / codeine / pseudoephedrine)
  • codeine
  • Decohistine Expectorant (codeine / guaifenesin / pseudoephedrine)
  • Deconamine CX (guaifenesin / hydrocodone / pseudoephedrine)
  • Hydrocod-GF (guaifenesin / hydrocodone)
  • hydrocodone
  • Lomanate (atropine / diphenoxylate)
  • Lomocot (atropine / diphenoxylate)
  • Lomotil (atropine / diphenoxylate)
  • Lonox (atropine / diphenoxylate)
  • lopinavir / ritonavir
  • lorazepam
  • Hydrocodone CP (chlorpheniramine / hydrocodone / phenylephrine)
  • Equetro (carbamazepine)
  • ETH-Oxydose (oxycodone)
  • Exalgo (hydromorphone)
  • Kadian (morphine)

It is worth bearing in mind that the above list is only a fraction of the 699 medicines known to interact with Tasimelteon, and that patients should inform doctors of their entire drug regimen to rule out any potential interactions.


Some patients have reported changes in behavior resulting in abnormal thinking when under the influence of sedatives and hypnotics like Tasimelteon. These changes can include aggressiveness, agitation and hallucinations. Patients with a history of depression could potentially experience severe mood swings or even suicidal thoughts. Therapy with this medication should therefore be administered under great caution in patients with depression or any major psychiatric disorder, and patients should be monitored for changes in behaviour or mood. Pharmacists and healthcare professionals are advised against dispensing large quantities of medicine to these patients as a means of reducing the risk of suicide by overdose.

Patients are advised to avoid drinking alcohol, and to avoid using recreational drugs which could impair perception. The potential for intoxication, faint-headedness and dizziness is increased under these circumstances, and could pose a risk to the safety of the patient.

Tasimelteon should only be taken by pregnant women if the benefits of doing so are deemed to outweigh any potential risks, as studies in animals have shown evidence of embryofetal toxicity as a direct result of using this medication. Adverse effects included delayed ossification, delayed physical development, reduced fetal body weight and significant neuro-behavioral impairment at doses equal to or greater than the standard recommended human dose.

Because this medication is excreted into breastmilk, mothers who are currently breastfeeding are advised to either temporarily stop taking Tasimelteon until the infant reaches a non-nursing age, or to suspend nursing indefinitely and switch to formula.


Tasimelteon should be stored in a safe, dry place out of the reach of children, such as a dedicated locked medicine cabinet. In addition to this, the manufacturer recommends that Tasimelteon be kept out of direct sunlight and away from heat and moisture. It is therefore unsuitable for storage in the bathroom.

If a patient and doctor reach the conclusion that treatment with Tasimelteon is no longer necessary, the patient should dispose of their unwanted leftover medication in a thoughtful, safe and hygienic manner, such as delivering it to a pharmacy which operates a medication takeback scheme. This ensures that the medicine does not end up being inadvertently swallowed by animals or unwittingly discovered by children or adults.


Tasimelteon is a relatively new medication which has been successful in the treatment of non-24-hour sleep-wake disorder in those with impaired vision or complete blindness. It may also be useful as a means of combating jet lag or insomnia due to unnatural work shift patterns, although it is not yet fully approved for these conditions and may only be prescribed as such "off label"by a qualified physician.

Because Tasimelteon has the potential to worsen depression or mania in patients with a pre-existing history of mental illness, it should not be prescribed in great quantities to those with a history of psychiatric illness. To gain the best possible results from this medicine, patient and doctor are advised to work together to ascertain the optimal dose.

Last Reviewed:
December 26, 2017
Last Updated:
April 05, 2018
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