Tasimelteon side effects: what 5,770 FDA adverse event reports show

Tasimelteon · Hetlioz, Hetlioz Lq · 79 reaction terms · 7,255 drug–reaction co-reports · data 2026-09-14

Drug class

Melatonin Receptor Agonist

FDA label (Established Pharmacologic Class)

Brand names

Hetlioz, Hetlioz Lq

openFDA label

Who reports

5,770 reports · 10% serious · 166 with death outcome · 57% female

openFDA FAERS counts, all years, deduplication not applied

Used for

HETLIOZ is a melatonin receptor agonist. HETLIOZ capsules are indicated for the treatment of: Non-24-Hour Sleep-Wake Disorder (Non-24) in adults ( 1 ) Nighttime sleep disturbances in Smith-Magenis Syndrome (SMS) in patients 16 years of age and older ( .

FDA label, Indications and Usage

What it is

HETLIOZ contains tasimelteon, a melatonin receptor agonist, chemically designated as (1 R , 2 R )-N-[2- (2,3-dihydrobenzofuran-4-yl)cyclopropylmethyl]propanamide, containing two chiral centers.

FDA label, Description section

Boxed warning

None in the current label

How to read this page. FAERS is a spontaneous-reporting system: counts are not incidence rates and a signal is not proof of causation. Each reaction below is run through an automated screen — is the term in the FDA label (known), in the indications (the disease being treated), an administrative/coding term, or none of these (unlabeled)? That screen is mechanical text matching, not a causality assessment. The 30 hand-written Bradford Hill assessments are on the causality assessment page. Not medical advice.

Causality screen of the 36 strongest signals

Labeled adverse reaction 4Labeled (related wording) 2Likely indication confounding 2Reporting / coding artifact 16Not in label — unassessed 12

What the badges mean

Labeled adverse reaction The exact term appears in the label's warnings or adverse-reactions sections: a known, expected effect. The FAERS signal confirms the label rather than discovering anything.
Labeled (related wording) The label describes this effect under different wording (e.g. 'neutropenia' for 'neutrophil count decreased'). Treated as known.
Likely indication confounding The term appears in the label's indications: reports probably describe the disease being treated (or its progression), not a drug effect. Classic confounding by indication.
Reporting / coding artifact An administrative, monitoring or exposure term (product issue, off-label use, 'test normal', overdose...). Not a biological reaction; a high PRR here reflects how reports are coded.
Not in label — unassessed Not found in the label text, not an artifact pattern. This is a genuine candidate for a formal causality assessment (Bradford Hill / WHO-UMC); it has NOT had one here.

Strongest disproportionality signals

Flagged terms (PRR ≥ 2, χ² ≥ 4, n ≥ 10), ranked by PRR; infinite PRRs (no comparator reports) excluded. The EBGM column is a second, shrinkage-based estimate (MGPS) with its 5th percentile EB05 and the BCPNN IC025; a pair flagged by PRR alone is marked PRR-only and should be read as fragile. The strata column recomputes the PRR on serious reports only and flags pairs whose reports are unusually skewed by sex or come mostly from consumers rather than clinicians. 43 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.

Show: hide coding/lab/outcome terms hide indication terms unlabeled only hide PRR-only

Reaction	Reports	PRR 95% CI · ROR · χ²/p	EBGM EB05 · IC025	Label screen	Serious-only & strata	Trial cross-check
Middle insomnia	414	82.7 75.3–90.9ROR 89.0 · χ² 32,618 / p <1e-300	80.6 EB05 74.3 · IC025 +6.0 3/3 methods agree	Not in label — unassessed	serious PRR 33.0	no trial data cached
Initial insomnia	153	55.3 47.3–64.8ROR 56.8 · χ² 7,991 / p <1e-300	54.2 EB05 47.3 · IC025 +5.3 3/3 methods agree	Not in label — unassessed	serious n=3	no trial data cached
Incorrect product administration duration	165	29.8 25.6–34.6ROR 30.6 · χ² 4,528 / p <1e-300	29.5 EB05 25.9 · IC025 +4.5 3/3 methods agree	Reporting / coding artifact	serious n=1	no trial data cached
Abnormal dreams	223	29.4 25.8–33.4ROR 30.5 · χ² 6,044 / p <1e-300	29.1 EB05 26.0 · IC025 +4.6 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 8.7	no trial data cached
Nightmare	268	28.2 25.1–31.7ROR 29.6 · χ² 6,969 / p <1e-300	28.0 EB05 25.3 · IC025 +4.5 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 8.9	no trial data cached
Poor quality sleep	154	26.3 22.5–30.8ROR 27.0 · χ² 3,705 / p <1e-300	26.1 EB05 22.8 · IC025 +4.3 3/3 methods agree	Reporting / coding artifact	serious PRR 6.9	no trial data cached
Therapeutic product effect decreased	196	16.1 14.0–18.5ROR 16.6 · χ² 2,757 / p <1e-300	16.0 EB05 14.2 · IC025 +3.7 3/3 methods agree	Reporting / coding artifact	serious PRR 5.4	no trial data cached
Hypersomnia	88	11.2 9.1–13.8ROR 11.4 · χ² 806 / p 1e-177	11.0 EB05 9.1 · IC025 +3.0 3/3 methods agree	Not in label — unassessed	serious PRR 2.6	no trial data cached
Insomnia (trouble sleeping)	728	9.9 9.3–10.6ROR 11.2 · χ² 5,905 / p <1e-300	9.9 EB05 9.3 · IC025 +3.2 3/3 methods agree	Labeled (related wording) related wording	serious PRR 3.6	no trial data cached
Sleep disorder	188	9.8 8.5–11.3ROR 10.1 · χ² 1,475 / p <1e-300	9.7 EB05 8.5 · IC025 +3.0 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious PRR 1.9 · 73% consumer	no trial data cached
Drug effect less than expected	32	8.3 5.8–11.7ROR 8.3 · χ² 197 / p 5e-45	7.6 EB05 5.6 · IC025 +2.3 3/3 methods agree	Reporting / coding artifact	75% consumer	no trial data cached
Incorrect drug administration duration	61	7.8 6.1–10.0ROR 7.9 · χ² 354 / p 3e-79	7.4 EB05 6.0 · IC025 +2.5 3/3 methods agree	Reporting / coding artifact	serious PRR 2.0	no trial data cached
Product dose omission	138	7.6 6.4–8.9ROR 7.7 · χ² 783 / p 1e-172	7.4 EB05 6.4 · IC025 +2.6 3/3 methods agree	Reporting / coding artifact	serious PRR 34.7	no trial data cached
Somnolence (drowsiness)	408	7.4 6.7–8.1ROR 7.9 · χ² 2,264 / p <1e-300	7.3 EB05 6.7 · IC025 +2.7 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 2.3	no trial data cached
Product dose omission issue	480	6.1 5.6–6.7ROR 6.6 · χ² 2,083 / p <1e-300	6.1 EB05 5.6 · IC025 +2.5 3/3 methods agree	Reporting / coding artifact	serious PRR 4.3 · 80% consumer	no trial data cached
Nocturia (night-time urination)	16	4.8 2.9–7.8ROR 4.8 · χ² 44 / p 1e-11	4.3 EB05 2.8 · IC025 +1.3 3/3 methods agree	Not in label — unassessed	–	no trial data cached
Drug ineffective (drug did not work)	1,635	4.5 4.3–4.7ROR 5.9 · χ² 4,768 / p <1e-300	4.5 EB05 4.3 · IC025 +2.1 3/3 methods agree	Reporting / coding artifact	serious PRR 1.0	no trial data cached
Seasonal allergy	16	4.1 2.5–6.7ROR 4.1 · χ² 35 / p 2e-9	3.7 EB05 2.5 · IC025 +1.1 3/3 methods agree	Not in label — unassessed	–	no trial data cached
Inappropriate schedule of product administration	179	3.7 3.2–4.3ROR 3.8 · χ² 350 / p 3e-78	3.6 EB05 3.2 · IC025 +1.6 3/3 methods agree	Reporting / coding artifact	serious PRR 1.4 · 74% consumer	no trial data cached
Intentional dose omission	25	3.3 2.2–4.9ROR 3.3 · χ² 38 / p 3e-10	3.2 EB05 2.3 · IC025 +1.0 3/3 methods agree	Reporting / coding artifact	serious PRR 1.5	no trial data cached
Drug effect decreased	49	3.3 2.5–4.3ROR 3.3 · χ² 75 / p 3e-18	3.2 EB05 2.5 · IC025 +1.2 3/3 methods agree	Reporting / coding artifact	serious PRR 7.6	no trial data cached
Product dose omission in error	23	3.1 2.1–4.7ROR 3.1 · χ² 31 / p 1e-8	3.0 EB05 2.1 · IC025 +0.9 3/3 methods agree	Reporting / coding artifact	serious PRR 3.0 · 91% consumer	no trial data cached
Migraine	76	2.9 2.3–3.6ROR 2.9 · χ² 94 / p 2e-22	2.9 EB05 2.4 · IC025 +1.1 3/3 methods agree	Not in label — unassessed	serious PRR 2.1	no trial data cached
Sleep apnoea syndrome	15	2.9 1.7–4.7ROR 2.9 · χ² 16 / p 3e-5	2.7 EB05 1.7 · IC025 +0.6	Not in label — unassessed	serious PRR 2.5	no trial data cached
Therapeutic product effect incomplete	49	2.5 1.9–3.3ROR 2.5 · χ² 44 / p 2e-11	2.5 EB05 2.0 · IC025 +0.8	Reporting / coding artifact	–	no trial data cached
Disturbance in attention	37	2.5 1.8–3.4ROR 2.5 · χ² 31 / p 1e-8	2.4 EB05 1.9 · IC025 +0.7	Likely indication confounding shares a disease stem with the indications wording	serious PRR 0.6	no trial data cached
Restlessness	25	2.5 1.7–3.7ROR 2.5 · χ² 21 / p 3e-6	2.4 EB05 1.7 · IC025 +0.6	Not in label — unassessed	–	no trial data cached
Headache	386	2.2 2.0–2.5ROR 2.3 · χ² 272 / p 2e-61	2.2 EB05 2.1 · IC025 +1.0 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 0.9	no trial data cached
Illness	61	2.2 1.7–2.8ROR 2.2 · χ² 39 / p 2e-10	2.2 EB05 1.8 · IC025 +0.7	Reporting / coding artifact	serious PRR 0.4 · ♀ 80% (drug 57%) · 79% consumer	no trial data cached
Restless legs syndrome	11	2.2 1.2–4.0ROR 2.2 · χ² 6 / p 0.007	2.1 EB05 1.3 · IC025 +0.0	Not in label — unassessed	serious PRR 3.6	no trial data cached
Product administration error	12	2.2 1.2–3.8ROR 2.2 · χ² 7 / p 0.005	2.1 EB05 1.3 · IC025 +0.1	Reporting / coding artifact	–	no trial data cached
Hallucination (hallucinations)	45	2.2 1.6–2.9ROR 2.2 · χ² 28 / p 7e-8	2.2 EB05 1.7 · IC025 +0.6	Not in label — unassessed	serious PRR 1.7	no trial data cached
Psychomotor hyperactivity	10	2.2 1.2–4.1ROR 2.2 · χ² 5 / p 0.011	2.1 EB05 1.2 · IC025 -0.0 PRR-only: not supported by EBGM or IC	Not in label — unassessed	–	no trial data cached
Ear infection	15	2.1 1.2–3.4ROR 2.1 · χ² 7 / p 0.004	2.0 EB05 1.3 · IC025 +0.1	Labeled (related wording) related wording	–	no trial data cached
Adverse event	51	2.0 1.5–2.6ROR 2.0 · χ² 25 / p 3e-7	2.0 EB05 1.6 · IC025 +0.5	Reporting / coding artifact	serious PRR 1.0	no trial data cached
Mood altered	15	2.0 1.2–3.3ROR 2.0 · χ² 7 / p 0.005	1.9 EB05 1.3 · IC025 +0.1	Not in label — unassessed	serious PRR 3.9	no trial data cached

Trial evidence (ClinicalTrials.gov)

Trial cross-check not yet run for this drug (ClinicalTrials.gov pull covers the 800 most-reported drugs first).

Most frequently reported reactions

By raw co-report count, regardless of disproportionality. Common terms here are often the illness itself or generic outcomes.

Reaction	Reports	PRR 95% CI · ROR · χ²/p	EBGM EB05 · IC025	Label screen	Serious-only & strata	Trial cross-check
Drug ineffective (drug did not work)	1,635	4.5 4.3–4.7ROR 5.9 · χ² 4,768 / p <1e-300	4.5 EB05 4.3 · IC025 +2.1 3/3 methods agree	Reporting / coding artifact	serious PRR 1.0	no trial data cached
Insomnia (trouble sleeping)	728	9.9 9.3–10.6ROR 11.2 · χ² 5,905 / p <1e-300	9.9 EB05 9.3 · IC025 +3.2 3/3 methods agree	Labeled (related wording) related wording	serious PRR 3.6	no trial data cached
Product dose omission issue	480	6.1 5.6–6.7ROR 6.6 · χ² 2,083 / p <1e-300	6.1 EB05 5.6 · IC025 +2.5 3/3 methods agree	Reporting / coding artifact	serious PRR 4.3 · 80% consumer	no trial data cached
Middle insomnia	414	82.7 75.3–90.9ROR 89.0 · χ² 32,618 / p <1e-300	80.6 EB05 74.3 · IC025 +6.0 3/3 methods agree	Not in label — unassessed	serious PRR 33.0	no trial data cached
Somnolence (drowsiness)	408	7.4 6.7–8.1ROR 7.9 · χ² 2,264 / p <1e-300	7.3 EB05 6.7 · IC025 +2.7 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 2.3	no trial data cached
Headache	386	2.2 2.0–2.5ROR 2.3 · χ² 272 / p 2e-61	2.2 EB05 2.1 · IC025 +1.0 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 0.9	no trial data cached
Nightmare	268	28.2 25.1–31.7ROR 29.6 · χ² 6,969 / p <1e-300	28.0 EB05 25.3 · IC025 +4.5 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 8.9	no trial data cached
Abnormal dreams	223	29.4 25.8–33.4ROR 30.5 · χ² 6,044 / p <1e-300	29.1 EB05 26.0 · IC025 +4.6 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 8.7	no trial data cached
Therapeutic product effect decreased	196	16.1 14.0–18.5ROR 16.6 · χ² 2,757 / p <1e-300	16.0 EB05 14.2 · IC025 +3.7 3/3 methods agree	Reporting / coding artifact	serious PRR 5.4	no trial data cached
Sleep disorder	188	9.8 8.5–11.3ROR 10.1 · χ² 1,475 / p <1e-300	9.7 EB05 8.5 · IC025 +3.0 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious PRR 1.9 · 73% consumer	no trial data cached
Inappropriate schedule of product administration	179	3.7 3.2–4.3ROR 3.8 · χ² 350 / p 3e-78	3.6 EB05 3.2 · IC025 +1.6 3/3 methods agree	Reporting / coding artifact	serious PRR 1.4 · 74% consumer	no trial data cached
Incorrect product administration duration	165	29.8 25.6–34.6ROR 30.6 · χ² 4,528 / p <1e-300	29.5 EB05 25.9 · IC025 +4.5 3/3 methods agree	Reporting / coding artifact	serious n=1	no trial data cached
Poor quality sleep	154	26.3 22.5–30.8ROR 27.0 · χ² 3,705 / p <1e-300	26.1 EB05 22.8 · IC025 +4.3 3/3 methods agree	Reporting / coding artifact	serious PRR 6.9	no trial data cached
Initial insomnia	153	55.3 47.3–64.8ROR 56.8 · χ² 7,991 / p <1e-300	54.2 EB05 47.3 · IC025 +5.3 3/3 methods agree	Not in label — unassessed	serious n=3	no trial data cached
Product dose omission	138	7.6 6.4–8.9ROR 7.7 · χ² 783 / p 1e-172	7.4 EB05 6.4 · IC025 +2.6 3/3 methods agree	Reporting / coding artifact	serious PRR 34.7	no trial data cached

Unlabeled candidate signals

These flagged terms were not found in the FDA label text and do not match an artifact pattern. They are the pairs that would merit a structured assessment (temporality, dose-response, biological plausibility, consistency across databases, trial or cohort evidence). The screen has not done that; string-matching misses label wording, and a strong PRR can still be stimulated reporting, co-medication, or the disease itself.

Middle insomnia — n=414, PRR 82.7
Initial insomnia — n=153, PRR 55.3
Hypersomnia — n=88, PRR 11.2
Migraine — n=76, PRR 2.9
Restlessness — n=25, PRR 2.5
Hallucination — n=45, PRR 2.2

Want to assess one of these properly? The runbook describes the Bradford Hill / trial-evidence workflow used on the assessment page, and handoff_top1000_signals.csv lists the strongest unassessed pairs across all drugs.

Common questions

What are the most reported side effects of Tasimelteon?

In FDA FAERS, the most frequently co-reported reaction terms for Tasimelteon are insomnia, middle insomnia, somnolence, headache, nightmare, abnormal dreams. These are report counts, not rates: FAERS has no denominator, reporting is voluntary and uneven, and a term can be reported because of the illness being treated rather than the drug.

Does Tasimelteon have an FDA boxed warning?

No. The FDA label retrieved for Tasimelteon has no boxed warning; see the label's Warnings and Precautions for the recognised risks.

Do FAERS signals prove that Tasimelteon causes these side effects?

No. A disproportionality signal (PRR, ROR) means a reaction is reported more often with this drug than with others in the database. That can reflect a real effect, but also the disease being treated, stimulated reporting after news or litigation, co-medications, or how reports are coded. Causality needs temporality, dose-response, biological plausibility, consistency across data sources and, ideally, trial or cohort evidence. This page screens each term against the FDA label and ClinicalTrials.gov results; it does not establish causation.

Sources & methods

FDA label via openFDA (set ID ca4a9b63-708e-49e9-8f9b-010625443b90, effective 20260804; matched on openfda.generic_name.exact:"TASIMELTEON")
Bayesian shrinkage measures computed offline over all 1,317,300 cached pairs: BCPNN information component (IC, with Norén closed-form IC025) and MGPS empirical-Bayes geometric mean (EBGM, EB05) with a two-component gamma prior fitted by maximum marginal likelihood (α₁=0.57, β₁=0.02, α₂=1.42, β₂=0.70, w=0.17); unstratified
FAERS pair statistics from the OpenPV build of 2026-09-14 (openFDA count= aggregation, field patient.drug.openfda.generic_name.exact, 79 reaction terms, min 3 co-reports); PRR/ROR with 95% CI, chi-square with Yates correction
Serious-only and stratified counts (serious:1, patient.patientsex, primarysource.qualification) from openFDA count queries; serious-only PRR uses the drug serious report total and the term global serious total (N_serious=11,882,979); strata shown only when n ≥ 20
Seriousness and sex counts from openFDA count=serious, patient.patientsex, seriousnessdeath

Page generated 2026-10-08. Label and PubChem text are retrieved automatically and may lag the current label; always check the current prescribing information. OpenPV is a beta research tool of the Open Source Medicine Foundation.