The US Food and Drug Administration (FDA) says it cannot approve Vanda Pharmaceuticals Inc.’s supplemental New Drug Application (sNDA) for tasimelteon (HETLIOZ) for the treatment of jet lag disorder in its current form.1
Although acknowledging positive efficacy signals from the JET trial data, the agency concluded there was insufficient comparability between the study’s phase advance models, simulating bedtime shifts of 5 and 8 hours, and real-world jet travel, which may include additional confounding factors.1
In a statement, the pharmaceutical company wrote, “Vanda respectfully disagrees with this interpretation,” and “maintains that the submitted dataset meets the statutory standard for substantial evidence of effectiveness on clinically relevant endpoints, for jet lag disorder.”1
Previously, in October 2025, Vanda and the FDA had entered a collaborative framework agreement where the agency committed to an expedited re-review of the sNDA by January 7, 2026, including consideration of narrowed, sleep-focused indications.1
According to the ICSD-3 criteria, core circadian misalignment is the primary driver of the jet lag disorder’s hallmark symptoms. As such, Vanda cites previous circadian rhythm which showed phase advance models were valid and reliable surrogates for stimulating core circadian misalignment. Their perspective posits circadian rhythm alone can serve as an analogous measure to jet lag, without the need to implement reduced oxygen pressure, physical constraints, noise, and lighting changes.1
JET study investigator, Sandra P. Smieszek, PhD, of Vanda Pharmaceutical, and colleagues wrote in the original publication, “These confounders could be reduced by directly assessing the treatment effect of tasimelteon on what is thought to be the underlying cause of the Essential Features of jet lag—the misalignment of the endogenous circadian timing system with that of the external environment—using a phase advance study design.”2
The JET study was a multicenter, randomized, double-blind, placebo-controlled, parallel-group investigation of tasimelteon on jet lag disorder utilizing said phase advance study design.2
Participants first underwent a 5 or 8-hour phase advance, followed by polysomnography (PSG) assessment. In a separate observational travel component, eligible individuals were flown from the US to the UK on a commercial nonstop, overnight transatlantic flight involving a 5- or 8-hour time zone change from baseline.²
During a second travel period, participants again traveled from the US to the UK and were randomized in a 1:1 ratio to receive either tasimelteon 20 mg or placebo, administered 30 minutes (±15 minutes) before their habitual bedtime based on their time zone of origin.²
Investigators collected subjective assessments Patient Global Impression of Severity Scale (PGI-S), the Karolinska Sleepiness Scale (KSS), and the post-sleep questionnaire (PSQ). The prespecified primary endpoint was total sleep time in the first two-thirds of the night, most likely to be disrupted as measured by PSG. Secondary subjective outcomes measured by sleep diaries included subjective total sleep time (TSTs) and subjective sleep quality.2
The study enrolled 48 adults aged 18–75 years without a history of primary insomnia or sleep disorders other than jet lag. Eligibility for evaluation required a Jet Lag Symptom Scale (JLSS) total score of ≥4. Of these participants, 25 completed both study phases and were included in the modified intent-to-treat population (tasimelteon, n = 13; placebo, n = 12).²
Overall, tasimelteon treatment was associated with an increase in objective total sleep time in the first two-thirds of the night on night 3, with a mean change from baseline of 34.8 minutes (95% CI, 2.6–66.9; P = .0354).²
On day 4, PGI-S scores were significantly improved with tasimelteon compared with placebo (between-group difference, −0.63; 95% CI, −1.1 to −0.1; P = .0168). Additionally, on night 3, subjective TSTs were significantly improved with tasimelteon versus placebo, with a between-group difference of 78.45 minutes (95% CI, 12.2–144.7; P = .0225). Across all 3 nights, cumulative TSTs were significantly greater with tasimelteon compared with placebo (between-group difference, 174.9 minutes; 95% CI, 6.7–343.2; P = .0423).²
Investigators also observed statistically significant correlations between PSG measures on night 3 and subjective outcomes, including sleep quality (Pearson r = 0.46; P <.01) and PGI-S scores (Pearson r = 0.52; P <.007).²
Vanda stated it intends to continue working constructively with the FDA and will pursue available procedural pathways to advance tasimelteon for the treatment of jet lag disorder.¹
ReferencesVanda Pharmaceuticals . Vanda Pharmaceuticals Announces Receipt of FDA Decision Letter on HETLIOZ® Supplemental New Drug Application for Jet Lag Disorder. Prnewswire.com. Published January 8, 2026. Accessed January 8, 2026. https://www.prnewswire.com/news-releases/vanda-pharmaceuticals-announces-receipt-of-fda-decision-letter-on-hetlioz-supplemental-new-drug-application-for-jet-lag-disorder-302656392.htmlPolymeropoulos CM, Polymeropoulos VM, Czeisler EL, et al. Once-daily tasimelteon (VEC-162) for jet lag following transmeridian travel: A multicenter, randomized, double-blind, placebo-controlled trial. Frontiers in Neurology. 2022;13. doi:https://doi.org/10.3389/fneur.2022.901467