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Tasimelteon Side Effects

The most commonly reported side effects of tasimelteon include insomnia, product dose omission issue, and middle insomnia, based on 5,763 FDA adverse event reports from 2014 to 2025. 28.4% of reports found the drug to be ineffective.

#1 Reported: InsomniaAll side effects ↓Top Co-Medication: Sodium-oxybateDrug interactions ↓76% of Reports Are AdultDemographics ↓

Tasimelteon side effects

Percentages show how often each reaction appears relative to total reports for tasimelteon.

1
Drug Ineffective28.4%1,635
2
Insomnia12.6%727
3
Product Dose Omission Issue8.3%480
4
Middle Insomnia7.1%412
5
Somnolence7.1%408
6
Headache6.7%384
7
Nightmare4.7%268
8
Abnormal Dreams3.9%223
9
Fatigue3.9%222
10
Therapeutic Product Effect Decreased3.4%196
11
Sleep Disorder3.3%188
12
Inappropriate Schedule Of Product Administration3.1%179
13
Incorrect Product Administration Duration2.9%165
14
Poor Quality Sleep2.7%154
15
Initial Insomnia2.7%153

These are voluntary reports and do not establish that tasimelteon caused these reactions.

Report severity

10.3%Serious595 reports
4.9%Hospitalizations282 reports
2.9%Fatal166 reports

Seriousness is determined by the reporter, not by OpenClaim.

Tasimelteon drug interactions

Other drugs that appear in adverse event reports alongside tasimelteon. Drugs flagged as a suspected cause appear in the first column. Drugs taken at the same time but not suspected appear in the second.

Also suspected

1
Sodium-oxybate0.2%14
2
Alprazolam0.2%10
3
Aripiprazole0.2%10
4
Escitalopram-oxalate0.2%10
5
Quetiapine-fumarate0.1%7
6
Bupropion0.1%7
7
Clonazepam0.1%6
8
Semaglutide<0.1%5
9
Fluoxetine-hydrochloride<0.1%4
10
Acetaminophen<0.1%4
11
Gabapentin<0.1%4
12
Mirtazapine<0.1%4
13
Lithium<0.1%4
14
Rifampin<0.1%3
15
Sertraline-hydrochloride<0.1%3

Taken alongside

1
Ergocalciferol8.2%470
2
Levothyroxine-sodium6.5%376
3
Gabapentin6.1%353
4
Acetaminophen5.8%337
5
Omeprazole5.8%332
6
Atorvastatin-calcium5.4%311
7
Aspirin5.3%303
8
Metformin4.6%267
9
Lisinopril4.3%250
10
Amlodipine4.2%242
11
Alprazolam4.1%236
12
Clonazepam4.0%230
13
Metoprolol3.8%218
14
Trazodone-hydrochloride3.7%211
15
Fluticasone3.5%203

Co-occurrence in adverse event reports does not establish a drug interaction. Patients often take multiple medications, and these lists reflect prescribing patterns rather than causal relationships. Consult a healthcare provider about potential drug interactions.

Who reports tasimelteon side effects

56.7% of tasimelteon adverse event reports involve female patients and 42.8% involve male patients. The largest age group is adult at 76%. These figures reflect who reports side effects, not underlying risk.

Sex

Female56.7%
Male42.8%
Unknown0.5%

Age group

< 20.0%
2–110.4%
12–170.5%
18–6476.1%
65+22.9%

What is tasimelteon used for

Conditions and purposes for which patients were taking tasimelteon when the adverse event was reported.

Adjustment Disorder With Mixed Anxiety And Depressed MoodAsthmaAsthmaAttention Deficit Hyperactivity DisorderAutism Spectrum DisorderBipolar Ii DisorderBlindnessBrain Neoplasm MalignantBipolar DisorderBlindnessBlindness CorticalCentral-alveolar HypoventilationCircadian Rhythm Sleep DisorderChromosomal DeletionCircadian Rhythm Sleep Disorder

Showing 15 of 58 indications

Tasimelteon brand names and reporting trend

Tasimelteon is sold under the brand name Hetlioz Lq.

Brand names

Hetlioz Lq23

Quarterly reports (2014–2025)

20142016202020242025

An upward trend reflects increased FAERS reporting overall, not necessarily increased risk.

Taking tasimelteon with another medication?

Ask OpenClaim about your specific drug combination. Get a sourced report using FDA data, drug labels, and medical literature.

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