In August 2023, the share price of a major sleep apnoea device manufacturer fell by more than a third in a few weeks. The reason was a hypothesis. Investors had decided that weight management medications would shrink the market for CPAP machines, because obesity was assumed to be the dominant driver of obstructive sleep apnoea. Fix the weight, the logic went, and the sleep problem goes with it.
The hypothesis turned out to be wrong, and the reason it was wrong is the same reason a lot of patients on weight management therapy are not getting the results they expected. Sleep and weight are not a one-way street. They are a system, with traffic running both directions, and treating one without the other is the clinical equivalent of fighting with one hand behind your back.
What the company data actually showed
By early 2026, the same sleep device manufacturer had pulled three years of claims data on roughly 1.95 million patients and reported a finding that surprised the market (these are ResMed company-reported claims-data figures, not peer-reviewed research). Patients prescribed a weight management medication were 10 to 11 per cent more likely to start CPAP therapy than patients who were not, and they were stickier with it at three years. The chief executive’s summary in the January 2026 earnings call was that the headwind thesis was completely gone.
This was not because weight loss does not improve sleep apnoea. It does. The SURMOUNT-OSA trial, published in 2024, showed that a dual-incretin weight management medication reduced apnoea events per hour by 27 to 30 over 52 weeks, with around half of participants achieving disease resolution. That is a real and clinically meaningful effect.
The reason the company data surprised the market is that the half of trial participants who did not achieve resolution still needed treatment. Their sleep apnoea was not primarily about weight. It was about something else.
Why weight is only part of the OSA story
Around half of obstructive sleep apnoea cases in adults are attributable to excess weight, leaving roughly half that are not. The other drivers matter.
Craniofacial anatomy plays a substantial role. Naturally smaller mandibles, narrow upper airways, recessed jaws: these are largely inherited and not something weight loss will change. Ageing matters too. Upper airway muscle tone declines from midlife. Fat distribution around the neck and tongue changes. Menopausal hormonal shifts alter both airway tissue and respiratory drive. And around 70 per cent of OSA patients have at least one neurological or physiological contributor unrelated to weight, including a low arousal threshold or unstable ventilatory control during sleep.
A person who develops OSA in their fifties and assumes the weight they have gained is the reason may have the causation partly inverted. Their airway has been changing on a timeline that has very little to do with what they have eaten.
The reverse direction is where it gets interesting
The assumption that weight drives sleep has a reverse version that is at least as well evidenced and gets discussed far less. Sleep, including the disrupted sleep that OSA produces, independently drives weight.
The mechanism is well-mapped. Short sleep increases ghrelin (the hunger hormone) and reduces leptin (the satiety hormone) within twenty-four hours. It increases insulin resistance within days. It shifts food preference toward higher-calorie, higher-carbohydrate options through changes in reward processing.
The question is how much weight this actually accounts for. Until recently the answer was inferred from population studies. In 2022, a randomised controlled trial in JAMA Internal Medicine gave a much sharper number.
What sleep alone can do, in numbers
Eighty adults with overweight who habitually slept less than 6.5 hours a night were randomised to either a single sleep hygiene counselling session targeting 8.5 hours in bed, or to continue as normal. After two weeks, the sleep extension group slept 1.2 hours more per night on average, spontaneously ate 270 fewer calories per day, had no change in energy expenditure, and produced a real negative energy balance with measurable weight loss in two weeks.
If a 270 kcal/day deficit were sustained over a year, the cumulative effect would be substantial. Real-world adaptation would shrink it, but the realistic translation is somewhere in the order of 4 to 8 kg of weight movement per year from sleep extension alone, in people who were chronically under-sleeping. That is in the same range as several pharmaceutical interventions, achieved without a script.
The longitudinal cohort data supports this. A meta-analysis of 285,452 adults found short sleep duration carried a 35 per cent increased risk of obesity over follow-up. Laboratory sleep restriction studies show 253 to 385 kcal/day increases in food intake, with no compensatory rise in energy expenditure.
Why this matters for people on weight management therapy
Here is where the picture gets clinically uncomfortable.
Weight management medications work largely by reducing appetite. They lower hunger, increase satiety, and decrease the brain’s responsiveness to food cues. They are, in effect, doing the same thing that adequate sleep does, through a different mechanism.
If a patient on weight management therapy is also chronically under-sleeping, they are simultaneously taking a medication that reduces appetite while running a behavioural pattern that increases it. The medication wins on average, which is why people still lose weight. But the result is blunted compared to what it would be if sleep were addressed alongside the script.
This may be one of the reasons that patient response to weight management therapy varies so widely. A patient sleeping 5 hours a night with untreated sleep apnoea is fighting a 250 to 400 kcal/day metabolic headwind that no one has measured or named. Their weight loss is real but slower, the motivation to exercise is harder to sustain, and the cycle compounds.
What the multi-pronged approach actually looks like
We are not arguing that sleep should replace weight management therapy. The clinical evidence on these medications for weight loss and for OSA is strong, and for the right patient they are the right intervention.
What we are arguing is that treating weight without treating sleep is leaving a substantial lever on the table. The combination of approaches is supported by both directions of evidence. Weight loss reduces OSA severity in the portion of patients whose OSA is weight-driven. Sleep improvement reduces caloric intake independent of any other change. Treating sleep apnoea, when present, addresses an underlying driver that weight loss alone may not fully resolve. And patients who treat both report better adherence to all components, possibly because each is reinforcing the other.
The investor data from the device manufacturer captured this without trying to. Patients on weight management medications who also got CPAP were more engaged with both treatments and stayed on both longer. The system worked better when both halves were treated.
What this should change in the conversation
If you are on weight management therapy and your results are slower than you expected, the question worth asking is not just whether the dose is right. It is also whether you are sleeping enough, whether you are sleeping well, and whether anyone has investigated sleep-disordered breathing. The symptoms worth raising with a GP include snoring, observed pauses in breathing overnight, daytime sleepiness despite adequate hours in bed, and waking unrefreshed.
A home sleep study has become considerably more accessible in Australia in recent years, and a diagnosis changes the calculation. It moves the question from how do I lose more weight to what is actually driving this system, and which levers will move it furthest.
For patients in their forties and fifties particularly, where ageing-related airway changes are a real and underappreciated driver, the assumption that weight is the only relevant variable can be the thing keeping the weight on.
What we think matters
Weight, sleep, and metabolic health form a system. The evidence shows traffic running in every direction. Weight gain disrupts sleep, poor sleep increases appetite and weight, and treating either improves the other but rarely resolves it alone.
For most patients with weight to lose, the question is not weight management therapy or sleep, but both, in the right order, with both being addressed clinically. A weight management medication doing 80 per cent of the work it could do, because an upstream sleep problem is undoing some of the gain, is not a treatment failure. It is an incomplete plan.
If you have not had your sleep evaluated and you are working hard on the weight side, that is the next conversation. Not as a replacement for what you are already doing, but as the missing half that lets the rest of the plan reach its potential.
References used in this piece are listed in the sources section. This article does not constitute medical advice. Speak with your treating clinician about any health decisions.