The narcolepsy drug approved in August now has its phase 3 numbers in print

When the FDA approved oveporexton for narcolepsy type 1 on 5 August, the manufacturer disclosed that its two phase 3 trials had reached statistical significance but did not publish the effect sizes [s2]. Those numbers are now in the New England Journal of Medicine, and they show a large effect on the trials' main measures of wakefulness and cataplexy, alongside side effects in the large majority of patients who took the drug [s1]. We covered the approval itself in the drug's US clearance; this is what the pivotal evidence behind it actually says.

Narcolepsy type 1 develops when the brain loses most of the neurons that make orexin (also called hypocretin), a chemical that stabilises wakefulness and holds REM sleep to its proper place. Patients live with overwhelming daytime sleepiness, cataplexy — a sudden loss of muscle tone triggered by emotion — and broken nighttime sleep. Oveporexton (TAK-861) is an oral agonist that binds the orexin receptor 2 directly, replacing the missing signal rather than working around it with a stimulant or a sedative [s1].

What the two trials tested

The trials, called First Light and Radiant Light, enrolled participants aged 16 to 70 with narcolepsy type 1 and ran for 12 weeks [s1]. First Light randomly assigned 168 participants in a 3:3:2 ratio to twice-daily oveporexton at 1 mg or 2 mg, or to placebo; Radiant Light assigned 105 participants in a 2:1 ratio to twice-daily 2 mg or placebo [s1].

The primary endpoint was the change in mean sleep latency on the Maintenance of Wakefulness Test — how long a person can stay awake in a dim, quiet room, scored from 0 to 40 minutes, with 20 or more considered normal [s1]. This is an objective measure: it does not rely on a patient's own report of how alert they feel.

The size of the effect

On that wakefulness test, mean sleep latency improved by 14.3 to 19.8 minutes across the oveporexton groups, against a change of −0.4 to −0.8 minutes on placebo (adjusted P<0.001 for every comparison) [s1]. In other words, patients who could stay awake only a few minutes at baseline moved a large part of the way toward a normal score, while placebo groups did not move at all.

The subjective measure agreed. On the Epworth Sleepiness Scale — a 0-to-24 questionnaire on which under 10 is normal — oveporexton groups fell by 9.7 to 11.8 points, against 1.5 to 1.7 on placebo [s1]. Cataplexy, the symptom patients often find most disabling, fell by a median of 79.0% to 88.8% per week on the drug, against 27.7% to 39.1% on placebo [s1]. A placebo response of roughly a third is a reminder that cataplexy counts are noisy and expectation-sensitive; the drug's effect sits well above it.

The side effects are not incidental

Adverse events occurred in 86% to 89% of participants taking oveporexton, against 43% to 54% on placebo [s1]. The most common were increased urinary frequency and transient insomnia, each affecting a majority of those on the drug [s1]. This is the trade-off the approval data already hinted at: a drug that restores daytime wakefulness by switching orexin signalling back on can also make it harder to sleep at night and send patients to the bathroom more often. Both effects follow directly from what orexin does, and neither is a reason on its own to withhold a treatment for a disorder this disabling — but they are common enough that they belong in any first conversation about the drug.

What the trials do not settle

Twelve weeks is short for a medicine intended for life. The trials establish that oveporexton works and is broadly tolerable over three months; they do not speak to how the benefit, or the urinary and sleep side effects, hold up over years, nor to rarer harms that only large post-marketing populations reveal. Narcolepsy type 1 carries real long-term stakes — a 25-year US veterans cohort found markedly higher mortality among patients with the disorder — so whether earlier, more complete symptom control changes that trajectory is a question these trials were not built to answer. Both were funded by the manufacturer, Takeda [s1].

Sources

• [s1] Oveporexton for Narcolepsy Type 1 — Results from Two Phase 3 Trials, The New England Journal of Medicine, 9 September 2026.
• [s2] U.S. FDA Approves Takeda's ORZEYFUL (oveporexton), Takeda Pharmaceutical Company Limited, 5 August 2026.