CPAP for Sleep Apnoea: How It Works and What to Expect

If a sleep study has shown you have moderate or severe obstructive sleep apnoea (OSA), CPAP — continuous positive airway pressure — is the treatment your sleep clinic will almost certainly offer first. It is the most effective, best-studied therapy in sleep medicine, and recent evidence links regular use with substantially lower mortality.

Two clarifications before anything else. First, CPAP is a treatment for sleep apnoea, not for simple snoring — if you snore without breathing pauses or daytime sleepiness, CPAP is not the answer, and other pages on this site will serve you better. Second, CPAP only works while you use it, which is why so much of this article is about actually wearing the thing.

What CPAP is — and when it’s indicated

A CPAP machine is a small bedside pump that delivers a continuous stream of gently pressurised air through a hose and mask. That air pressure acts as a pneumatic splint, holding your throat open so it cannot collapse and interrupt breathing — which also abolishes the vibration that causes snoring in the process.

Clinical guidance from the American Academy of Sleep Medicine strongly recommends positive airway pressure therapy for adults with OSA.^[1] Severity is graded by the apnoea-hypopnoea index (AHI), the number of breathing disturbances per hour: on the NHS scale, 5–14 is mild, 15–30 moderate and over 30 severe.^[2] CPAP is the standard of care at the moderate-to-severe end; for milder disease, or for snoring without apnoea, other options are usually considered first.

Not sure which side of that line you’re on? Start with our guide to snoring versus sleep apnoea.

Does CPAP actually work? Strong evidence

For controlling the breathing events themselves, CPAP is the benchmark against which everything else is measured. The more important question is whether that translates into health.

The landmark long-term data came from Marin and colleagues in The Lancet in 2005. Following 1,651 men for ten years, they found that men with untreated severe OSA suffered fatal cardiovascular events at a rate of 1.06 per 100 person-years versus 0.55 in healthy controls, and non-fatal events at 2.13 versus 0.89 — and that CPAP treatment reduced this excess risk.^[3]

In March 2025, a much larger synthesis arrived: a meta-analysis in The Lancet Respiratory Medicine pooling 30 studies and over a million patients, with around five years’ average follow-up. It found CPAP use was associated with 37% lower all-cause mortality and 55% lower cardiovascular death, with a dose-response relationship — the more hours per night people used CPAP, the greater the benefit.^[4][5] In the interests of transparency: this study was supported by ResMed, a CPAP manufacturer, so read it with that in mind — though it is consistent with the independent evidence above.

For context on why untreated OSA is worth taking seriously in the first place, see our article on the health risks of snoring.

CPAP or APAP — what’s the difference?

Standard CPAP delivers one fixed pressure all night, determined during setup. APAP (automatic positive airway pressure) adjusts the pressure breath by breath within a set range, responding to what your airway is doing — less pressure when you don’t need it, more when you do.

Does the fancier version work better? Not meaningfully. The AASM guideline treats CPAP and APAP as equivalent, with comparable adherence and outcomes,^[1] and comparative studies bear this out.^[6] If your clinic offers APAP for home titration or comfort, that’s fine; if you’re on fixed-pressure CPAP and doing well, there’s no evidence-based reason to switch.

The adherence problem — and what actually helps

Here is CPAP’s honest weakness: it only works when it’s on your face. Struggling in the early weeks is common — masks can feel claustrophobic, air pressure takes getting used to, and some people quietly give up.

The evidence offers two useful facts. First, the AASM guideline found that educational interventions — understanding what OSA is, what CPAP does, and what to expect — measurably improve adherence, and it recommends education and support alongside the machine, not just a box handed over.^[1] So use your sleep service: ask questions, report problems, go to the follow-ups.

Second, the early weeks matter disproportionately. Research on adherence determinants shows that early patterns of use predict long-term use.^[7] Treat the first month as the habit-forming window: persist nightly, and raise niggles (mask discomfort, dryness, pressure issues) with your clinic promptly rather than soldiering on or quietly stopping. Mask and comfort problems are exactly what sleep services are set up to troubleshoot — that support is part of the treatment.^[1]

If you can’t tolerate CPAP: the alternatives

Some people genuinely cannot get on with CPAP despite good support. That is not a dead end — and it’s far better to use an alternative than to abandon treatment altogether.

Mandibular advancement devices (MADs). Custom-fitted mouthpieces that hold the lower jaw forward. CPAP lowers the AHI more, but MADs deliver comparable improvements in symptoms and quality of life, and people often wear them for more of the night.^[8] In the 2024 CRESCENT trial of 220 patients with hypertension and moderate-to-severe OSA, a custom MAD proved non-inferior to CPAP for 24-hour blood pressure reduction over six months, with longer nightly wear.^[9] Our anti-snoring devices guide covers them in depth.

Hypoglossal nerve stimulation. An implanted device that stimulates the nerve controlling the tongue, keeping the airway open — an option for selected people with moderate-to-severe OSA who cannot tolerate CPAP. In the STAR trial, median AHI fell 68% at twelve months.^[10] See our surgery guide for details.

Tirzepatide (Zepbound). For people with obesity and moderate-to-severe OSA, the weight-loss medication tirzepatide reduced AHI by 55–63% in the phase-3 SURMOUNT-OSA trials,^[11] and in December 2024 became the first drug approved by the US FDA for OSA.^[12] Our latest research round-up tracks this fast-moving area.

Getting CPAP in the UK

In the UK, CPAP for diagnosed sleep apnoea is available on the NHS. The pathway runs through your GP: describe your symptoms (partner-witnessed pauses, gasping, daytime sleepiness), and you can be referred to a sleep clinic, where testing is often done with a home device that monitors your breathing and heart rate while you sleep; results are graded by AHI.^[2] Our when to see a doctor guide walks through the referral conversation and what sleep studies involve.

The bottom line

For moderate-to-severe sleep apnoea, CPAP remains the gold standard: it controls the breathing events, improves how you feel, and is associated with substantially lower cardiovascular and overall mortality in long-term data.^[3][4] Its one great weakness is that it does nothing from the bedside drawer. Get educated, use your sleep service’s support, persist through the first month — and if you truly can’t tolerate it, switch to an evidence-backed alternative rather than giving up on treatment.