tasimelteon
Brand names: Hetlioz
Tasimelteon (Hetlioz) is a medicine that helps people with Non-24-Hour Sleep-Wake Disorder (Non-24) sleep better. It works by acting like melatonin in your body.
Drug Pricing (NADAC)
Generic Price
$608.56/unit
Generic Available
Yes (3 manufacturers)
Pricing data from NADAC (CMS), effective September 18, 2024. Compare all drug costs →
What it does
Tasimelteon is used to treat Non-24-Hour Sleep-Wake Disorder (Non-24) in adults.
Common side effects
Headache, Increased liver enzyme (alanine aminotransferase), Nightmares or unusual dreams
Key warnings
After taking tasimelteon, limit your activities to getting ready for bed.
How It Works
Tasimelteon is a melatonin receptor agonist. This means it works like melatonin, a natural hormone in your body that helps regulate sleep. By acting like melatonin, tasimelteon helps to adjust your body's sleep-wake cycle.
How to Take It
Take one 20 mg capsule of tasimelteon one hour before bedtime. Take it at the same time every night. Do not take it with food. It may take weeks or months before you notice the full effect.
Pregnancy & Breastfeeding
There isn't enough information about using tasimelteon during pregnancy to know if it's safe. Talk to your doctor if you are pregnant or plan to become pregnant. It is not known if tasimelteon passes into breast milk, so discuss breastfeeding with your doctor.
Missed Dose
If you miss a dose, skip it and take your next dose at the regular time. Do not take two doses at once.
Storage
Store tasimelteon capsules at room temperature (68°F to 77°F), away from light and moisture.
Side Effects (from patient reports)
Based on 4,955 FDA adverse event reports.
FDA Adverse Event Report Analysis
Detailed analysis of 5,762 reports from the FDA Adverse Event Reporting System (FAERS). Reports span 2014–2025.
Total Reports
5,762
Death-Related Reports
166
Hospitalization Reports
281
Top Indication
Non-24-Hour Sleep-Wake Disorder
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 1 | DRUG INEFFECTIVE | 1,635 |
| 2 | INSOMNIA | 727 |
| 3 | PRODUCT DOSE OMISSION ISSUE | 480 |
| 4 | MIDDLE INSOMNIA | 412 |
| 5 | SOMNOLENCE | 408 |
| 6 | HEADACHE | 384 |
| 7 | NIGHTMARE | 268 |
| 8 | ABNORMAL DREAMS | 223 |
| 9 | FATIGUE | 222 |
| 10 | THERAPEUTIC PRODUCT EFFECT DECREASED | 196 |
| 11 | SLEEP DISORDER | 188 |
| 12 | INAPPROPRIATE SCHEDULE OF PRODUCT ADMINISTRATION | 179 |
| 13 | INCORRECT PRODUCT ADMINISTRATION DURATION | 165 |
| 14 | POOR QUALITY SLEEP | 154 |
| 15 | INITIAL INSOMNIA | 153 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) FDA FAERS (Adverse Event Reporting System) Reports are voluntary and do not establish causation
Serious Warnings
After taking tasimelteon, limit your activities to getting ready for bed. This medicine can make you sleepy and affect your ability to think clearly.
Known Drug Interactions
7 DRUG INTERACTIONS Strong CYP1A2 inhibitors (e.g., fluvoxamine): Avoid use of tasimelteon in combination with strong CYP1A2 inhibitors because of increased exposure ( 7.1 , 12.3 ) Strong CYP3A4 inducers (e.g., rifampin): Avoid use of tasimelteon in combination with rifampin or other CYP3A4 inducers, because of decreased exposure ( 7.2 , 12.3 ) 7.1 Strong CYP1A2 Inhibitors (e.g., fluvoxamine) Avoid use of tasimelteon in combination with fluvoxamine or other strong CYP1A2 inhibitors because of a potentially large increase in tasimelteon exposure and greater risk of adverse reactions [see Cli...
Mechanism: Rifampin causes your body to clear tasimelteon much faster than normal. This lowers the amount of medicine in your system and makes it less effective.
What to do: Avoid using these two drugs together. Rifampin will likely prevent tasimelteon from working correctly.
7 DRUG INTERACTIONS Strong CYP1A2 inhibitors (e.g., fluvoxamine): Avoid use of tasimelteon in combination with strong CYP1A2 inhibitors because of increased exposure ( 7.1 , 12.3 ) Strong CYP3A4 inducers (e.g., rifampin): Avoid use of tasimelteon in combination with rifampin or other CYP3A4 inducers, because of decreased exposure ( 7.2 , 12.3 ) 7.1 Strong CYP1A2 Inhibitors (e.g., fluvoxamine) Avoid use of tasimelteon in combination with fluvoxamine or other strong CYP1A2 inhibitors because of a potentially large increase in tasimelteon exposure and greater risk of adverse reactions [see Cli...
Mechanism: Fluvoxamine blocks the enzyme that normally breaks down tasimelteon. This causes tasimelteon to build up in your body, which increases the risk of side effects.
What to do: Do not take these two medications at the same time. Your doctor should find an alternative treatment to avoid high drug levels.
7.3 Beta-Adrenergic Receptor Antagonists (e.g., acebutolol, metoprolol) Beta-adrenergic receptor antagonists have been shown to reduce the production of melatonin via specific inhibition of beta-1 adrenergic receptors.
Mechanism: This heart medicine can lower the amount of natural sleep chemicals your body produces. This may stop the sleep medicine from working as well as it should.
What to do: Tell your doctor if your sleep medicine does not seem to be working while taking this heart medication. They may need to change your treatment plan.
7.3 Beta-Adrenergic Receptor Antagonists (e.g., acebutolol, metoprolol) Beta-adrenergic receptor antagonists have been shown to reduce the production of melatonin via specific inhibition of beta-1 adrenergic receptors.
Mechanism: Both of these products target the same sleep receptors in your brain. Using them together could cause excessive sleepiness or change how the prescription medicine works.
What to do: Talk to your doctor before taking over-the-counter melatonin with this prescription sleep medicine. They may advise you to avoid using both at the same time.
7.3 Beta-Adrenergic Receptor Antagonists (e.g., acebutolol, metoprolol) Beta-adrenergic receptor antagonists have been shown to reduce the production of melatonin via specific inhibition of beta-1 adrenergic receptors.
Mechanism: Acebutolol can lower the amount of natural melatonin your body makes. This may make tasimelteon less effective since it works on the same sleep system.
What to do: Your doctor may need to monitor your sleep patterns or adjust your medications if they are not working well.
Common Questions
What is tasimelteon used for?
How should I take tasimelteon?
What if I miss a dose?
Can tasimelteon cause side effects?
Is tasimelteon safe during pregnancy?
Can I take tasimelteon with food?
How long does it take for tasimelteon to work?
What should I avoid while taking tasimelteon?
How should I store tasimelteon?
Can I switch between the capsules and the liquid?
What are the common side effects of tasimelteon?
Does tasimelteon interact with other medications?
What drug class is tasimelteon?
Is tasimelteon safe during pregnancy?
Related Medications in Melatonin Receptor Agonist
Other drugs grouped near tasimelteon — same-class peers and common alternatives.
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suvorexant
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Medication Guides
Understanding Drug Interactions
How CYP450 enzymes, inhibitors, and inducers affect your medications
Generic vs Brand Name Drugs
FDA requirements, cost savings, and when the difference matters
Narrow Therapeutic Index Drugs
Why some drugs demand precise dosing and monitoring
Common Drug Interactions
Dangerous medication combinations and how to protect yourself
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What the FDA Data Shows for tasimelteon
The FDA label for tasimelteon (sold under brand names such as Hetlioz) classifies it as a prescription-only medication in the Melatonin Receptor Agonist class. Tasimelteon is used to treat Non-24-Hour Sleep-Wake Disorder (Non-24) in adults. Official labeling lists 5 commonly reported side effects, including Headache, Increased liver enzyme (alanine aminotransferase), Nightmares or unusual dreams.
Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 4,955 voluntary reports. The database also lists 5 documented drug interactions derived from FDA labeling, with the top-flagged interaction rated moderate severity. NADAC pricing from CMS shows a generic unit cost of $608.56.
Report counts do not establish causation — a FAERS entry documents a temporal association, not proof that the drug produced the outcome. Widely prescribed medications naturally accumulate more reports than niche therapies, so raw totals must be interpreted alongside total exposure. Shortage status, recall history, and patent information further shape supply and switching decisions. This page summarizes public FDA data for educational purposes only and is not a substitute for professional medical advice — always consult a licensed healthcare provider before starting, stopping, or changing any medication.
Data Sources
Drug labeling: FDA Drug Labels (SPL/DailyMed). Adverse events: FDA Adverse Event Reporting System (FAERS). Pricing: CMS National Average Drug Acquisition Cost (NADAC).
FAERS reports are voluntary and do not establish causation. Drug interactions are derived from FDA labeling and clinical references. Always consult a healthcare professional before making medication decisions.
Last updated: April 10, 2025
Read our methodology — how this data is sourced, computed, and verified.
All federal data sources used on this page
- FDA Orange Book — approved drug products with therapeutic equivalence. accessdata.fda.gov/cder/ob
- FDA DailyMed — NIH-hosted drug labeling for FDA-approved meds. dailymed.nlm.nih.gov
- FDA Adverse Event Reporting System (FAERS) — post-marketing safety surveillance. fda.gov/drugs/faers
- NLM RxNorm — standardized clinical drug nomenclature. nlm.nih.gov/research/umls/rxnorm
- CMS Medicare Part B Drug Average Sales Price Files — federal drug pricing data. cms.gov/medicare/part-b-drugs/asp
- FDA Drug Shortages Database — current and resolved drug shortage tracking. accessdata.fda.gov/drugshortages