Prescription medication · Melatonin Receptor Agonist
tasimelteon
Also sold as Hetlioz. Tasimelteon is used to treat Non-24-Hour Sleep-Wake Disorder (Non-24) in adults.
Data updated 2026-05-15
- 5,762
- FDA reportsLightly reported
- 5
- InteractionsFew interactions
- $608.56
- Generic price (NADAC)
What the data shows
tasimelteon (Hetlioz) is a prescription Melatonin Receptor Agonist, reported less often than most tracked drugs (5,762 FDA reports), with 5 documented drug interactions.
Reporting volume reflects how widely a drug is used and studied, not how dangerous it is, a FAERS report documents a temporal association, never proof of cause.
tasimelteon (Hetlioz) is a prescription Melatonin Receptor Agonist. Tasimelteon is used to treat Non-24-Hour Sleep-Wake Disorder (Non-24) in adults.
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.
Verify with FDA → · CMS NADAC pricing →
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.
The sections below are summarized in plain English from tasimelteon's FDA-approved prescribing information. They describe what the official label says, and are not personal medical advice.
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.
This is a plain-language summary of tasimelteon's FDA labeling, not individualized dosing advice. Ask a pharmacist or prescriber before changing how you take this medication.
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.
This is a plain-language summary of tasimelteon's FDA labeling, not individualized advice. Ask a pharmacist or prescriber about pregnancy or breastfeeding on this medication.
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.
This is a plain-language summary of tasimelteon's FDA labeling, not individualized advice. Ask a pharmacist or prescriber what to do about your specific missed dose.
Storage
Store tasimelteon capsules at room temperature (68°F to 77°F), away from light and moisture.
Side Effects (from patient reports)
Based on 5,762 FDA adverse event reports.
Most-reported reactions
Adverse reactions in FAERS for tasimelteon, by number of reports
- Trouble falling asleep or staying asleep
Trouble falling asleep or staying asleep
727 reports
- Waking up in the middle of the night
Waking up in the middle of the night
412 reports
- Sleepiness
Sleepiness
408 reports
- Headache
Headache
384 reports
- Nightmare 268
Nightmare
268 reports
- Unusual dreams 223
Unusual dreams
223 reports
- Tiredness 222
Tiredness
222 reports
- The medicine is not working as well 196
The medicine is not working as well
196 reports
- Problem with sleep 188
Problem with sleep
188 reports
- Taking the medicine at the wrong time 179
Taking the medicine at the wrong time
179 reports
What this shows Bars show how often each reaction was reported, not how likely it is to happen, a report records a temporal association, never proof that the drug caused it.
Reports over time
Adverse-event reports filed for tasimelteon each year to the FDA Adverse Event Reporting System (FAERS).
Year-to-year volume tracks usage, prescribing, and scrutiny, not a change in per-patient risk. Source: FDA FAERS.
Where tasimelteon sits
tasimelteon has more FDA adverse-event reports than 27% of the drugs FAERS tracks. A high position reflects how widely a drug is used and watched, not how dangerous it is.
Percentile across all drugs PlainMeds tracks by FAERS report volume. The dot is tasimelteon; the line is the median (50th percentile).
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
Reports Mentioning Death
166
2.9% of reports — not proof of cause
Hospitalization Reports
281
Top Indication
Non-24-Hour Sleep-Wake Disorder
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 2 | INSOMNIA | 727 |
| 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 |
| 16 | NAUSEA | 145 |
| 17 | PRODUCT DOSE OMISSION | 138 |
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...
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...
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.
This is a plain-language summary of interactions documented in FDA labeling, not individualized advice. Ask a pharmacist or prescriber before combining medications.
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?
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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 5,762 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.
Data currency: FDA FAERS adverse-event reports through 2025, CMS NADAC acquisition-cost pricing effective December 2024, compiled and last refreshed May 2026. See our methodology for per-source dates and refresh cadence. Spot a figure that looks wrong? Report a correction.
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