A Phase 2/3 interventional study of cleminorexton and Placebo in Narcolepsy Type 1 and Narcolepsy Type 2, sponsored by Centessa Pharmaceuticals (UK) Limited. Recruiting at 26 sites in United States. Open to participants aged 18 Years to 70 Years. Per ClinicalTrials.gov, last updated 2026-11-03.
Sponsored by Centessa Pharmaceuticals (UK) Limited · Phase 2/3, Interventional, and Treatment
Narcolepsy Type 1 (NT1) and Narcolepsy Type 2 (NT2) are rare conditions that make people feel very sleepy during the day (often referred to as excessive daytime sleepiness [EDS]). People living with these conditions might find it hard to stay alert and pay attention when they are at school, working, driving, or performing other daily activities.
While all conditions result in feeling sleepy, there are some differences in other common symptoms:
Orexin is a protein in the brain that helps coordinate a system that plays an important role in helping people to stay awake during the daytime. Cleminorexton is designed to mimic the action of orexin. The purpose of this study is to see how safe and tolerable cleminorexton is in NT1 and NT2 and learn about what the drug does to the body. Another goal of the study is to see if cleminorexton can help people with NT1 and NT2 feel less sleepy and make other symptoms better.
The SAPPHIRE Clinical Trial
The Sponsor may in the future, through a protocol amendment, expand the protocol to include participants with idiopathic hypersomnia (IH) in Cohort C.
157 studies on the registry are indexed under Narcolepsy; 37 are open to participants now.
This study's planned enrollment of 222 is above the median of 78 across 114 interventional studies indexed under Narcolepsy.
Browse Narcolepsy studies →Centessa Pharmaceuticals (UK) Limited is the lead sponsor of 6 studies on the registry; 5 are open to participants now.
Compared within Narcolepsy, this study's primary condition as ClinicalTrials.gg classifies it; the registry's first condition term is Disorders of Excessive Somnolence. The counts are of registry records indexed under each term, refreshed daily. How we classify →
Key Inclusion Criteria:
Key Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
BMI (body mass index)
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Cancer (malignancy)
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Drug: cleminorexton
Drug: cleminorexton
Drug: Placebo
Drug: cleminorexton
Drug: cleminorexton
Drug: Placebo
Oral cleminorexton capsule
matching placebo capsule
Change from baseline in mean sleep latency (average of the first 4 trials) on the Maintenance of Wakefulness Test (MWT)
Time frame: Baseline to week 12
Change from baseline in Epworth Sleepiness Scale (ESS) total score
Time frame: Baseline to Week 12
Weekly Cataplexy Rate (WCR)
Measurement specific to Group A
Time frame: Week 12
Change from baseline in Narcolepsy Severity Scale for Clinical Trials (NSS-CT)
Measurement specific to Group A
Time frame: Baseline to Week 12
Change from baseline in Narcolepsy Severity Scale-2 for Clinical Trials (NSS2-CT) total score
Measurement specific to Group B
Time frame: Baseline to Week 12
Incidence, Severity, and casual relationship of participants with Treatment Emergent Adverse Events (TEAEs)
Time frame: Baseline to Week 12
Number of participants with abnormal changes from baseline in clinical laboratory tests
Time frame: Baseline to Week 12
Number of participants with abnormal changes from baseline in vital signs
Time frame: Baseline to Week 12
Number of participants with abnormal changes from baseline in 12-lead electrocardiograms (ECGs)
Time frame: Baseline to Week 12
Number of participants with at least 1 endorsement of Item 4 or 5 on Columbia-Suicide Severity Rating Scale (C-SSRS)
Time frame: Baseline to Week 12
Cmax: Maximum observed plasma concentration
Time frame: Baseline to Week 12
Tmax: Time of Maximum Concentration for cleminorexton
Time frame: Baseline to Week 12
AUC: Area under the plasma concentration-time curve
Time frame: Baseline to Week 12
Plan to share: No
No publications or documents are linked to this record.
Started May 2026 (actual). Primary completion is estimated for Sep 2027, 16 months after the start.
How these figures are worked out, and which studies are left out of them.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
Eligibility is decided by the study team. Share this record with your doctor or contact the team directly.
Contact study teamGet an email when the registry record changes — status, dates, results — or when someone posts here.
Sign in to followQuestions and observations about this study, from anyone following it. Not medical advice, and not a channel to the study team — their contact details are on the registry record.
Sign in to join the discussion. Reading takes no account; posting does. You choose a display name, and a pseudonym is the default.
Nothing here yet. If you are running this trial, taking part in it, or weighing whether to, this is the place to say so.
Centessa Pharmaceuticals (UK) Limited