A Pill for Sleep Apnea? Lancet Trial Shows 47% Fewer Breathing Pauses
A European phase 2 trial found the existing epilepsy drug sulthiame reduced sleep apnea breathing interruptions by up to 47%. It is not a replacement for CPAP yet, but it is the strongest signal yet that a pill-based approach may work.
Medically reviewed by Dr. Helena Vasquez, MD
Approved pharmacological treatments for obstructive sleep apnea do not exist. That sentence may change within a few years. A European phase 2 trial published in The Lancet found that sulthiame, an existing carbonic anhydrase inhibitor approved for childhood epilepsy, reduced apnea-hypopnea index by up to 47% in adults with moderate-to-severe disease (The Lancet, 2025).
Key Takeaways
- The FLOW trial enrolled 298 adults with moderate-to-severe obstructive sleep apnea across 28 European centers (The Lancet, 2025).
- Higher-dose sulthiame reduced breathing interruptions by up to 47% and improved overnight oxygen levels compared with placebo.
- Sulthiame is not FDA-approved for sleep apnea and remains investigational in the United States and Canada (Medical Daily, 2026).
How Does Sulthiame Work?
Obstructive sleep apnea occurs when upper airway muscles relax during sleep and collapse the airway. Most drug attempts have tried to stiffen those muscles directly, with limited success. Sulthiame takes a different route: it stabilizes the brain's ventilatory control system and increases respiratory drive, which reduces the likelihood of airway collapse (University of Gothenburg, 2026).
Citation capsule: Sulthiame is a carbonic anhydrase inhibitor that improves ventilatory response and upper airway muscle tone, and was previously approved for benign childhood epilepsy before being repurposed for sleep apnea trials (The Lancet, 2025).
What Did the FLOW Trial Find?
The trial was multicenter, randomized, double-blind, and placebo-controlled. Participants received placebo or one of several sulthiame doses for a defined treatment period. The primary outcome was the apnea-hypopnea index. Higher doses produced up to 47% fewer breathing interruptions, and overnight oxygen saturation improved compared with placebo. Side effects were mostly mild and temporary (The Lancet, 2025).
Citation capsule: In the FLOW trial, patients receiving higher doses of sulthiame experienced up to 47% fewer breathing interruptions during sleep compared with those given placebo, along with improved overnight oxygen levels (Medical Daily, 2026).
Why Does This Matter When CPAP Already Exists?
CPAP remains the most effective treatment for obstructive sleep apnea when used consistently. The problem is adherence: up to 50% of patients stop using CPAP within a year because of mask discomfort, noise, claustrophobia, or travel inconvenience (Medical Daily, 2026). A once-daily pill that meaningfully reduces breathing interruptions without a mask would fill a gap for the millions who cannot or will not tolerate CPAP. Tirzepatide reduces apnea severity in obese patients, but through weight loss rather than a direct mechanism on airway stability (Medical Daily, 2026).
What Are the Limitations?
FLOW is a phase 2 dose-finding study, not a phase 3 efficacy confirmation trial. Sulthiame has not been approved for sleep apnea anywhere in the world, and the FDA has not set a timeline for review. The trial also measured short-term outcomes; long-term safety in sleep apnea patients is not yet established (DrugBank, 2026).
Frequently Asked Questions
Can I get sulthiame for sleep apnea today?
Not in the United States or Canada. It is an investigational drug for this indication and is available only through clinical trials (Medical Daily, 2026).
Does sulthiame replace CPAP?
Not yet. CPAP is still the gold standard for patients who tolerate it. Sulthiame may become an option for patients who cannot use CPAP or who need additional therapy, but that depends on phase 3 results and regulatory approval (Medical Daily, 2026).
Is sulthiame safe?
In the FLOW trial, adverse effects were mostly mild and temporary. The drug has been used for epilepsy in several countries, so its safety profile is documented, though not in sleep apnea patients over the long term (The Lancet, 2025).
How does sulthiame compare to weight-loss drugs for sleep apnea?
Tirzepatide and semaglutide can improve apnea by reducing weight. Sulthiame works directly on the breathing control mechanism regardless of body weight, which makes it conceptually distinct (Medical Daily, 2026).
Conclusion
The FLOW trial is the strongest evidence to date that a pill can meaningfully reduce sleep apnea severity. It does not replace CPAP, and it is not available yet. But for patients who abandon CPAP or never start it, sulthiame represents a plausible alternative if phase 3 data confirm the signal.
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