Drug side effects
tasimelteon Side Effects
The reactions most often reported to the FDA for tasimelteon (also sold as Hetlioz), with demographics, serious outcomes, and reporting trends.
Data updated 2026-05-15
- 5,762
- FAERS reports
Data from the FDA Adverse Event Reporting System (FAERS), 2014 to 2025. A FAERS report records a temporal association, not proof of cause. See our methodology for how figures are compiled and de-duplicated.
The most commonly reported side effects of tasimelteon come from 5,762 reports to the FDA, broken down here by frequency, patient demographics, and serious outcomes.
This page analyzes 5,762 reports to the FDA Adverse Event Reporting System (FAERS) for tasimelteon (Hetlioz): the reactions reported most often, who reported them, serious outcomes such as hospitalization, and year-over-year trends. A FAERS report does not prove the drug caused the effect, and report volume tracks how widely a drug is used, not how likely an effect is for any one person. Educational information, not medical advice.
Total Reports
5,762
Reports Mentioning Death
166
2.9% of reports — not proof the medicine caused the death
Hospitalizations
281
4.9% of reports
Top Indication
Non-24-Hour Sleep-Wake Disorder
Most Reported Adverse Reactions
Who Reports Side Effects
Gender Distribution
Age Distribution
Reporting Trend by Year
Reactions in Death Reports
Top reactions reported in 166 reports where death was an outcome. These are voluntarily reported and do not establish causation.
| Reaction | Reports |
|---|---|
| DEATH | 129 |
| CARDIAC ARREST | 4 |
| PNEUMONIA | 4 |
| CHRONIC OBSTRUCTIVE PULMONARY DISEASE | 3 |
| COMPLETED SUICIDE | 3 |
| SEPSIS | 3 |
| ACCIDENT | 2 |
| CARDIAC FAILURE | 2 |
| CARDIOVASCULAR DISORDER | 2 |
| DYSPHAGIA | 2 |
| HYPOTENSION | 2 |
| MYOCARDIAL INFARCTION | 2 |
| PNEUMONIA ASPIRATION | 2 |
| PULMONARY EMBOLISM | 2 |
| TOXICITY TO VARIOUS AGENTS | 2 |
| ACCIDENTAL DEATH | 1 |
| ACUTE MYOCARDIAL INFARCTION | 1 |
| AORTIC ANEURYSM | 1 |
| ARTERIOSCLEROSIS CORONARY ARTERY | 1 |
Reactions in Hospitalization Reports
Top reactions in 281 reports where hospitalization was an outcome.
| Reaction | Reports |
|---|---|
| FALL | 28 |
| PRODUCT DOSE OMISSION | 23 |
| PNEUMONIA | 18 |
| DRUG DOSE OMISSION | 13 |
| INSOMNIA | 12 |
| CARDIAC DISORDER | 10 |
| SOMNOLENCE | 10 |
| URINARY TRACT INFECTION | 10 |
| MALAISE | 9 |
| SEIZURE | 9 |
| MIDDLE INSOMNIA | 8 |
| DIZZINESS | 7 |
| NIGHTMARE | 7 |
| SEPSIS | 7 |
| THROMBOSIS | 7 |
| VOMITING | 7 |
| CEREBROVASCULAR ACCIDENT | 6 |
| CHEST PAIN | 6 |
Nearby, Related Medications
What the FAERS Data Reveals About tasimelteon Side Effects
The FDA Adverse Event Reporting System (FAERS) contains 5,762 voluntary reports linked to tasimelteon and its brand equivalents (Hetlioz), spanning 2014 through 2025. Of those, 166 (2.9%) listed death as an outcome and 281 (4.9%) involved hospitalization. The most common indication reported alongside adverse events was Non-24-Hour Sleep-Wake Disorder.
Demographic breakdowns help contextualize who is being exposed to the drug. Of reports with known sex, 57% were female and 43% male; age distribution skews toward 45-64, with 1,272 reports in that bracket. The single most reported reaction is insomnia with 727 submissions, followed by middle insomnia and somnolence.
How to read these numbers
FAERS is a signal-detection tool, not a scorecard. Reports are voluntary, and a single case may list multiple suspect drugs, so numbers above should not be read as incidence rates or per-patient risk. Widely prescribed drugs naturally accumulate more reports than niche therapies even when individual risk is low. These aggregates are useful for spotting patterns that merit further pharmacovigilance, not for choosing between medications. This page is for educational reference only and is not medical advice, speak with a licensed clinician about any side-effect concerns.
Drugs With a Similar FAERS Report Volume
Other medications with a total FDA adverse-event report count closest to tasimelteon's 5,762.
Read our methodology - how this data is sourced, computed, and verified.