On March 31, Eli Lilly announced a definitive agreement to acquire Centessa Pharmaceuticals for up to $7.8 billion — a deal that immediately became the largest single transaction in the emerging field of orexin-based sleep medicine. The acquisition signals that major pharmaceutical companies now view sleep-wake disorders as a frontier comparable in commercial and scientific significance to obesity and neurodegeneration.
What Lilly Is Buying
The centerpiece of the deal is cleminorexton (formerly ORX750), a once-daily oral orexin receptor 2 (OX2R) agonist. Unlike existing narcolepsy treatments — which primarily manage symptoms through stimulants or sodium oxybate — cleminorexton is designed to restore the brain's natural wakefulness signals by activating the same receptor system that is damaged or destroyed in narcolepsy.
Orexin neurons, located in the hypothalamus, produce neuropeptides that promote and stabilize wakefulness. In narcolepsy type 1, an autoimmune process destroys these neurons, leaving patients with uncontrollable sleepiness and, often, cataplexy — sudden episodes of muscle weakness triggered by emotions. Narcolepsy type 2 and idiopathic hypersomnia involve similar excessive sleepiness without the same degree of orexin neuron loss.
The Clinical Data
Centessa's Phase 2 program has tested cleminorexton across three conditions, and the results have drawn attention from analysts and competitors alike:
Narcolepsy Type 1: At the 1.5 mg dose, cleminorexton achieved a greater-than-20-minute placebo-adjusted improvement on the Maintenance of Wakefulness Test (MWT), a standard measure of a patient's ability to stay awake. The Epworth Sleepiness Scale (ESS) — a widely used self-report measure — dropped from 18 to 5, representing a shift from severe pathological sleepiness to near-normal. Weekly cataplexy episodes declined to an incidence rate ratio of 0.13.
Narcolepsy Type 2: At the 4 mg dose, the drug achieved a greater-than-10-minute placebo-adjusted MWT improvement, with clinically meaningful ESS reductions.
Idiopathic Hypersomnia: At the 2 mg dose, statistically significant and clinically meaningful improvements were observed across multiple efficacy measures in the first dosing cohort.
Adverse events across all cohorts were generally mild to moderate and transient: pollakiuria (51%), insomnia (22%), dizziness (13%), and headache (11%).
The Deal Structure
Lilly will pay $38.00 per share in cash at closing, representing an equity value of approximately $6.3 billion — a 40.5% premium to Centessa's 30-day volume-weighted average trading price. The deal also includes non-transferable contingent value rights (CVRs) worth up to an additional $9.00 per share (approximately $1.5 billion), tied to FDA approvals for narcolepsy type 2 and idiopathic hypersomnia indications before 2030.
The transaction is expected to close in the third quarter of 2026.
The Orexin Gold Rush
Lilly is not alone in pursuing orexin agonists. The competitive landscape has intensified rapidly:
- Takeda, which developed the orexin antagonist insomnia drug suvorexant (Belsomra), is developing its own orexin agonist program
- Alkermes recently acquired Avadel Pharmaceuticals for up to $2.1 billion to strengthen its narcolepsy portfolio and is advancing its own OX2R agonist into Phase 3
- Multiple smaller biotechs hold early-stage orexin programs
The race reflects a broader recognition that current narcolepsy treatments — stimulants like modafinil and pitolisant, and the controlled substance sodium oxybate — manage symptoms without addressing the underlying neurobiology. An orexin agonist that restores the missing wakefulness signal would represent a fundamentally different approach.
Beyond Narcolepsy
Centessa's pipeline extends beyond cleminorexton. ORX142, a second orexin agonist, is in early clinical development for neurological and neurodegenerative disorders — potentially including conditions where orexin dysfunction contributes to cognitive decline or disrupted sleep-wake cycles. A third compound, ORX489, is in preclinical development for neuropsychiatric disorders.
These pipeline assets suggest that Lilly sees orexin biology as relevant far beyond rare sleep disorders, potentially extending into Alzheimer's disease, Parkinson's disease, and other conditions where sleep-wake disruption is both a symptom and a possible disease accelerator.
What This Means for Patients
For the estimated 200,000 Americans living with narcolepsy — many of whom cycle through multiple medications with significant side effects — the orexin agonist approach offers the prospect of a treatment that works with the brain's own wakefulness system rather than overriding it with stimulants.
Cleminorexton's registrational (Phase 3) trials are expected to begin soon. If they confirm the Phase 2 results, and if the FDA grants approval, the drug could reach patients within the next few years. In the meantime, the sheer scale of Lilly's investment — and the competitive activity it has triggered — suggests that sleep medicine is entering a period of innovation not seen since the introduction of CPAP for sleep apnea decades ago.
