What Actually Happens When You Have Sleep Apnea

Sleep apnea is common, frequently undiagnosed, and widely misunderstood as simply "loud snoring."

The reality is a repeated disruption to breathing during sleep. In obstructive sleep apnea, the airway repeatedly narrows or closes, oxygen levels can fall and the brain has to keep intervening to restore breathing — sometimes dozens or even hundreds of times a night.

For years, treatment has largely centred on mechanically preventing that airway from collapsing. Now, for the first time, an oral drug designed to alter the neuromuscular problem behind obstructive sleep apnea has completed two Phase 3 trials and reached FDA review. That doesn't make CPAP obsolete. But it could make the future of sleep apnea treatment look considerably different.

TL;DR

• Obstructive sleep apnea (OSA) happens when the upper airway repeatedly narrows or collapses during sleep, reducing or temporarily stopping airflow.
• The brain repeatedly responds to these events, often causing brief arousals that restore breathing without the person consciously remembering waking up.
• Diagnosis usually involves a sleep study, with one important measurement being the apnea-hypopnea index (AHI): the average number of apneas and hypopneas per hour of sleep.
• Positive airway pressure, usually CPAP, remains one of the most established and effective treatments, but masks and nightly device use can be difficult for some people to tolerate.
• AD109 — also known by its proposed brand name Oxnimbi — could represent something genuinely new. The once-nightly oral treatment is designed to improve upper-airway muscle activity during sleep rather than mechanically splinting the airway open.
• Two Phase 3 trials have now produced significant reductions in breathing events. In SynAIRgy, the primary treatment-policy analysis found a 44.1% reduction in AHI after 26 weeks, versus 17.6% with placebo. The corresponding figures in LunAIRo were 33.7% and 7.3%.
• The larger headline reductions sometimes reported — 55.6% and 46.8% — come from on-treatment analyses, looking at the response while participants remained on the medication.
• Tolerability matters. Dry mouth, insomnia and nausea were among the most common treatment-related adverse effects, and more than one in five AD109 participants in each trial stopped treatment because of adverse events by six months.
• AD109 remains investigational. Its New Drug Application is under FDA review; it is not currently an approved replacement for CPAP.
• Untreated sleep apnea matters beyond tiredness, with OSA associated with hypertension, cardiovascular disease, impaired daytime functioning and other health consequences.

What's Actually Happening When You Have Sleep Apnea?

Obstructive sleep apnea occurs when the upper airway becomes too narrow or closes during sleep.

When you're awake, muscles surrounding the throat help maintain an open airway. During sleep, muscle activity naturally changes. In someone susceptible to OSA, the combination of airway anatomy and sleep-related reductions in muscle tone can allow the airway to narrow sufficiently to obstruct breathing. A complete or near-complete interruption is an apnea. A substantial reduction in airflow is a hypopnea.

As airflow falls, blood oxygen can drop and carbon dioxide can rise. Eventually the brain responds, briefly increasing wakefulness and muscle activation sufficiently to reopen the airway. Normal breathing returns. Then the person falls more deeply asleep again. And the process can repeat — in severe cases, dozens of times every hour.

The person experiencing it may remember none of those brief arousals, but their sleep has nevertheless been repeatedly fragmented. That's why someone can apparently spend eight hours in bed and still wake feeling as though they haven't slept properly.

Why Snoring Isn't the Same Thing as Sleep Apnea

Snoring and obstructive sleep apnea frequently occur together, but they're not interchangeable.

Snoring is produced when tissues in a narrowed upper airway vibrate as air passes through them. Someone can snore without repeatedly obstructing their breathing enough to meet the criteria for OSA. What's more concerning is loud snoring accompanied by pauses in breathing, choking or gasping, particularly when combined with symptoms such as persistent daytime sleepiness, morning headaches or problems concentrating. It's also why interventions aimed at the mouth and nose alone — including mouth taping — aren't a substitute for proper assessment.

Often, the first person to notice isn't the person with sleep apnea. It's the person sleeping next to them.

Obstructive and Central Sleep Apnea Aren't the Same

Most sleep apnea is obstructive, but there's another important form.

Obstructive sleep apnea occurs because airflow is physically obstructed despite continued respiratory effort. Central sleep apnea involves a problem with the signalling controlling breathing: respiratory effort itself temporarily stops because the brain isn't sending the appropriate signals to the breathing muscles. Some people can have features of both.

The distinction matters because causes and treatments differ. The discussion here — including CPAP alternatives and AD109 — primarily concerns obstructive sleep apnea.

How Sleep Apnea Is Actually Diagnosed

Symptoms can raise suspicion, but they aren't enough to diagnose OSA reliably. Fatigue, poor concentration, headaches and disrupted sleep can have many causes. Snoring alone doesn't establish the diagnosis either.

Assessment therefore usually involves an overnight sleep study. Depending on the person and circumstances, this may involve full polysomnography in a sleep laboratory or an appropriate home sleep apnea test. These tests can measure combinations of airflow, breathing effort, blood oxygen saturation, heart rate and sleep-related signals to determine whether breathing is repeatedly being disrupted.

One of the best-known measurements is the apnea-hypopnea index, or AHI, representing the average number of qualifying apneas and hypopneas occurring per hour of sleep. Broadly:

• 5–14.9 events per hour: mild OSA
• 15–29.9: moderate OSA
• 30 or more: severe OSA

AHI is useful, but it isn't the entire disease. Two people with similar AHI measurements can have different degrees of oxygen disturbance, daytime symptoms, cardiovascular risk and underlying physiology. Clinicians therefore interpret the number alongside symptoms and the wider clinical picture.

Why You Can Have Sleep Apnea Without Realising It

One reason OSA remains undiagnosed is that its defining events happen while you're asleep. The brain's brief responses to obstruction don't necessarily produce the kind of awakening you remember the next morning.

Instead, the clues may appear during the day: excessive sleepiness, persistent tiredness, poor concentration, irritability and morning headaches. Some people don't experience dramatic daytime symptoms at all.

There are also recognised risk factors. Obesity is a major one, although people without obesity can absolutely develop OSA. Age, upper-airway anatomy, craniofacial structure, neck characteristics and other factors can contribute. This is another reason the idea that sleep apnea is simply a consequence of being overweight is misleading — weight can matter enormously without explaining every case.

Why Untreated Sleep Apnea Matters Beyond Tiredness

The consequences aren't confined to whether you feel refreshed in the morning. OSA exposes the body to repeated cycles of airway obstruction, oxygen disturbance, arousal and sympathetic nervous-system activation.

Over time, obstructive sleep apnea is associated with hypertension and cardiovascular disease, while fragmented sleep can impair concentration, mood and daytime performance. Poor sleep also has knock-on effects elsewhere, including how your gut behaves and how much low-grade inflammation your body carries. Daytime sleepiness can also have immediate consequences — someone repeatedly deprived of restorative sleep may have impaired attention and reaction times, which matters particularly when driving or operating machinery.

Associations between OSA and long-term disease don't mean every person with untreated sleep apnea will develop cardiovascular disease. But they do explain why significant OSA is treated as a medical condition rather than simply an inconvenient form of snoring.

How Sleep Apnea Is Treated Now

Treatment depends on severity, symptoms, anatomy and the individual patient. For many people with clinically significant OSA, positive airway pressure therapy remains a central treatment.

CPAP — continuous positive airway pressure — delivers pressurised air through a mask while the person sleeps. The principle is surprisingly straightforward: instead of waiting for the airway to collapse, the pressure acts like a pneumatic splint, helping keep it open throughout sleep. When used consistently, CPAP can be extremely effective at preventing obstructive breathing events.

Its weakness isn't primarily whether it works. It's whether people can comfortably use it every night. Masks can leak. Some people feel claustrophobic. Others struggle with pressure, nasal symptoms, noise or simply the practical reality of sleeping attached to a device. These problems can sometimes be improved substantially through different masks, humidification, pressure adjustment and proper follow-up rather than abandoning treatment after an unsuccessful first attempt.

But the adherence problem is real. And it helps explain the continuing search for alternatives.

CPAP Isn't the Only Option

Depending on the type and severity of OSA, other approaches can include mandibular advancement devices, which reposition the lower jaw to help maintain an open airway. Positional therapy can help some people whose obstruction occurs predominantly while sleeping on their back. Weight loss can substantially improve OSA in people for whom excess weight is an important contributor, and newer obesity treatments have also changed this part of the treatment landscape. Selected patients may benefit from surgery or implanted hypoglossal nerve stimulation.

There isn't therefore one universal sleep-apnea treatment. The more interesting question is whether medication could become another major part of that toolkit.

Could Sleep Apnea Soon Be Treated With a Pill?

This is where the treatment landscape may be about to change.

AD109, also known by the proposed brand name Oxnimbi, is an investigational once-nightly oral treatment combining aroxybutynin and atomoxetine. Instead of mechanically holding the airway open, AD109 is designed to address an important component of the neuromuscular dysfunction involved in OSA. Its components act on neural pathways involved in maintaining upper-airway muscle activity during sleep, with the aim of improving airway muscle tone and making collapse less likely.

That distinction is important. CPAP mechanically prevents obstruction. AD109 attempts to alter part of the physiology that allows obstruction to happen. And this isn't based on a small preliminary study anymore — AD109 has completed two pivotal Phase 3 trials involving approximately 1,300 people with obstructive sleep apnea.

What Did the AD109 Trials Actually Find?

The two Phase 3 trials were called SynAIRgy and LunAIRo. Both compared AD109 with placebo and measured changes in AHI. SynAIRgy ran for six months, while LunAIRo continued for a year, with the primary efficacy endpoint assessed at 26 weeks in both studies.

The results need a little explanation because two sets of percentages are now circulating.

SynAIRgy. Under the trial's primary treatment-policy estimand, AD109 reduced AHI by 44.1% from baseline at 26 weeks, compared with a 17.6% reduction with placebo. An on-treatment analysis, which focuses on participants while they remained on treatment, produced a larger reduction of 55.6%, compared with 19.1% for placebo.

LunAIRo. The corresponding treatment-policy analysis found a 33.7% reduction in AHI with AD109, versus 7.3% with placebo. The on-treatment analysis found a 46.8% reduction, versus 6.8% with placebo.

Those distinctions matter. It would be accurate to say the trials produced reductions approaching or exceeding 50% among people analysed while taking the drug. But it would be misleading to present those larger numbers as though they were the primary treatment-policy results. The more conservative analyses incorporate what happens when people discontinue treatment — something particularly relevant here because tolerability proved to be an important part of the story.

Oxygen Levels Improved Too

AHI wasn't the only objective measurement to move. The trials also assessed hypoxic burden, which captures aspects of the depth and duration of oxygen desaturation associated with breathing disturbances.

Under the treatment-policy analysis, hypoxic burden fell by 44.7% in SynAIRgy and 37.4% in LunAIRo with AD109. Among participants analysed while on treatment, reductions were larger: 60.5% and 58.2%, respectively.

That's encouraging because OSA isn't simply about counting how many breathing events occur — the physiological consequences of those events, including how much they disturb oxygenation, matter too. But there's an important limit to what these data tell us. The Phase 3 trials weren't designed or powered to establish whether AD109 prevents heart attacks, strokes or other long-term cardiovascular outcomes. Improving a marker associated with cardiovascular risk isn't the same thing as proving that the treatment reduces cardiovascular events.

The Important Caveat: Side Effects and Discontinuation

An oral tablet sounds inherently easier than sleeping with a mask. The trials show why the comparison isn't that simple.

Dry mouth, insomnia and nausea were among the most commonly reported treatment-related adverse effects with AD109. More importantly, adverse effects caused a significant number of participants to stop treatment. In SynAIRgy, 21.2% of participants receiving AD109 discontinued because of adverse events by six months, compared with 3.1% receiving placebo. In LunAIRo, the corresponding figures at six months were 23.7% with AD109 and 6.6% with placebo. By 12 months, 28.6% of participants in the AD109 group had discontinued because of adverse events, compared with 10.0% receiving placebo. Insomnia was one notable contributor.

No serious adverse events or deaths were reported as related to AD109 across the two Phase 3 trials.

That's an important balance. The efficacy signal is real. So is the tolerability issue. And the difference between the treatment-policy and on-treatment efficacy results illustrates why both matter: a drug can work well while someone is taking it and still have its real-world effectiveness reduced if a meaningful proportion of people cannot comfortably remain on it.

Is AD109 Available Yet?

No. AD109 remains an investigational treatment and isn't currently an approved alternative to CPAP.

Apnimed submitted a New Drug Application to the US Food and Drug Administration in 2026, and the FDA subsequently accepted the application for review. That moves AD109 substantially beyond the category of an interesting experimental compound. But FDA review isn't FDA approval, and until a regulatory decision is made, the drug remains investigational.

If ultimately approved, however, it could represent something genuinely new: an oral pharmacological treatment aimed at the neuromuscular physiology contributing to obstructive sleep apnea. That would add another treatment mechanism to a field historically dominated by devices, physical interventions and, more recently, treatments addressing obesity where excess weight is a major driver.

Would a Pill Replace CPAP?

Probably not — and that isn't necessarily the right way to think about it.

OSA isn't one identical disease process occurring in every patient. For some people, airway anatomy may dominate. For others, obesity, sleep-related reductions in upper-airway muscle responsiveness or several interacting mechanisms may contribute. CPAP has an enormous advantage: when used correctly, positive airway pressure can mechanically prevent airway collapse regardless of some of those underlying differences. A medication targeting neuromuscular function may work better for some physiological patterns than others.

There's also the tolerability trade-off. A mask may be difficult for one person to live with. A tablet causing persistent dry mouth or insomnia may be worse for another. The future of OSA treatment may therefore be less about finding a universal replacement for CPAP and more about having enough effective options to match treatment to the individual.

What This Actually Means

If you suspect sleep apnea, diagnosis comes first. Persistent daytime sleepiness, morning headaches, loud snoring and witnessed pauses in breathing are reasons to seek assessment, but symptoms alone can't establish OSA.

Don't assume snoring automatically means sleep apnea. The two overlap, but they're not the same condition.

CPAP remains an extremely effective and established treatment. If the first experience with it is uncomfortable, mask choice, pressure settings, humidification and specialist support can make a substantial difference.

AD109 is genuinely significant, but it isn't an approved CPAP replacement. Two Phase 3 trials have demonstrated meaningful reductions in breathing disturbances and hypoxic burden, while also revealing a notable tolerability problem.

The larger efficacy numbers need context. The frequently reported 55.6% and 46.8% reductions came from on-treatment analyses. The corresponding primary treatment-policy reductions were 44.1% and 33.7%.

And perhaps most importantly, sleep apnea is more than snoring or feeling tired. Repeated airway obstruction changes what happens physiologically throughout the night, even if you don't remember waking up.

Frequently Asked Questions

What is sleep apnea?

Sleep apnea is a sleep-related breathing disorder in which breathing repeatedly stops or substantially decreases during sleep. In obstructive sleep apnea, this happens because the upper airway repeatedly narrows or collapses.

What are the main symptoms of sleep apnea?

Common clues include loud snoring, witnessed pauses in breathing, choking or gasping during sleep, excessive daytime sleepiness, morning headaches and difficulty concentrating. Some people have relatively few obvious daytime symptoms.

How is sleep apnea diagnosed?

Diagnosis generally involves an overnight sleep study, either through polysomnography in a sleep laboratory or an appropriate home sleep apnea test. One important measurement is AHI, the average number of apneas and hypopneas occurring per hour.

What counts as severe sleep apnea?

Using conventional AHI categories, 5–14.9 events per hour is mild OSA, 15–29.9 is moderate and 30 or more is severe. Clinicians also consider symptoms, oxygen disturbance and the wider health picture rather than relying exclusively on AHI.

Is snoring always sleep apnea?

No. People can snore without having OSA. Repeated breathing pauses, gasping and significant daytime symptoms make sleep apnea more concerning and warrant proper assessment.

Is CPAP the only treatment?

No. Depending on the individual, alternatives can include mandibular advancement devices, positional therapy, weight management, surgery and hypoglossal nerve stimulation. Positive airway pressure nevertheless remains one of the most established and effective treatments.

What is AD109?

AD109, proposed brand name Oxnimbi, is an investigational once-nightly oral treatment for obstructive sleep apnea. It combines aroxybutynin and atomoxetine and is designed to improve upper-airway muscle activity during sleep.

How effective was the new sleep apnea pill?

In the SynAIRgy Phase 3 trial, the primary treatment-policy analysis found a 44.1% reduction in AHI after 26 weeks with AD109, versus 17.6% with placebo. LunAIRo found a 33.7% reduction versus 7.3% with placebo. On-treatment analyses produced larger reductions of 55.6% and 46.8%, respectively.

What are the side effects of AD109?

Dry mouth, insomnia and nausea were among the most common treatment-related adverse effects in the Phase 3 programme. Treatment discontinuation because of adverse effects was also substantially more common with AD109 than placebo.

Can I get AD109 now?

No. AD109 remains investigational and isn't currently an approved treatment for OSA. Its New Drug Application is under FDA review.

Should I wait for new treatments before starting CPAP?

No. Untreated clinically significant OSA has real health consequences, and existing treatments can be highly effective. Someone diagnosed with OSA should discuss currently appropriate treatment with their clinician rather than leaving the condition untreated while waiting for an investigational therapy.

The Bottom Line

Sleep apnea isn't simply loud snoring.

In obstructive sleep apnea, the upper airway repeatedly narrows or collapses during sleep. Breathing falls, oxygen can drop, the brain responds and the airway reopens — only for the cycle potentially to begin again minutes later. Someone can experience this repeatedly throughout the night without remembering most of it. That's why diagnosis matters. And it's why treatment matters too.

Positive airway pressure remains one of the most effective ways of stopping that cycle, but its practical limitations have left a substantial need for additional treatments. AD109 is therefore genuinely interesting: two Phase 3 trials show that an oral treatment targeting upper-airway neuromuscular function can meaningfully reduce breathing disturbances and improve measures of nocturnal oxygenation.

The less exciting part of the story is equally important — adverse effects caused more than one in five treated participants to discontinue by six months in both trials. That's not a reason to dismiss the drug. It's a reason to describe it properly.

If approved, AD109 could give people with obstructive sleep apnea something the field has long lacked: an oral pharmacological option targeting part of the physiology behind airway collapse. It wouldn't mean the end of CPAP. It would mean another way to treat a condition that has never been as simple as snoring.

This is general information rather than medical advice. If you think you may have sleep apnea, speak to your GP or another qualified healthcare professional about appropriate assessment and treatment.

For the everyday sleep habits that sit around all of this, The Sleep Reset covers light, timing and wind-down routines, and the Reset Companion can help you apply them.

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