Roughly 12% of people using CPAP for sleep apnea still experience significant daytime sleepiness, even with consistent use. That number drops to about 6% after ruling out other sleep disorders and depression, but the frustration is real either way. If you’re doing everything right and still dragging through the day, several fixable problems could be at play.
Your Body May Need More Time
CPAP doesn’t flip a switch. Sleep specialists at Mayo Clinic note that it can take two to three months of regular use before you notice a meaningful decrease in daytime sleepiness. Some people need even longer. Years of fragmented sleep cause changes in your brain’s sleep regulation that don’t reverse overnight. If you’ve only been on CPAP for a few weeks and feel discouraged, that timeline alone may explain what you’re experiencing.
The general recommendation is to use your machine for at least four hours every night, ideally all night, for a full two to three months before judging whether it’s working. If you’re past the three-month mark with consistent use and still feel exhausted, that’s the point to start investigating other causes.
Your Machine Data May Hide Problems
Even when your machine reports a normal number of breathing events per hour (under 5), you can still have residual symptoms. Research comparing different types of positive airway pressure therapy found that patients with fully normalized scores still reported persistent daytime sleepiness, just at lower intensity than before treatment. In other words, good numbers on your machine don’t guarantee you’ll feel alert.
Mask leak is one common culprit that quietly undermines therapy. A leak rate above 24 liters per minute starts reducing comfort and treatment effectiveness. At 30 liters per minute, one study found the pressure response of auto-adjusting machines dropped by 56%, meaning your device literally can’t compensate properly for your breathing events. Most machines log leak data, and many will trigger an alert at 42 liters per minute or higher, but significant damage to sleep quality happens well before that alarm threshold. Check your app or machine display for leak trends, especially in the second half of the night when you’re more likely to shift position.
Mouth Breathing and Humidity Issues
If you use a nasal mask and your mouth falls open during sleep, the pressurized air escapes through your mouth instead of keeping your airway open. Up to 70% of nasal CPAP users report symptoms like nasal congestion, dry nose and throat, sneezing, and sore throat from dry air. People who breathe through their mouth for more than 70% of their sleep time have significantly lower compliance overall, often because the discomfort fragments their sleep without them realizing it.
A heated humidifier helps, but it can’t fully solve the problem. During mouth breathing, humidity inside the mask drops from around 81% to about 60%, even with the humidifier running. Cold, dry winter air makes this worse, since the ambient moisture level directly affects what reaches your airway. If you wake up with a dry mouth or sore throat regularly, consider switching to a full-face mask that covers both your nose and mouth, or adding a chin strap to keep your mouth closed.
Other Sleep Disorders Can Coexist
Sleep apnea isn’t always the only thing disrupting your sleep. When researchers screened CPAP users who remained sleepy, they found that half the cases could be explained by conditions like restless legs syndrome, depression, or narcolepsy. These conditions don’t show up on your CPAP data because they have nothing to do with breathing.
Upper airway resistance syndrome is another possibility that’s easy to miss. It causes repeated brief arousals throughout the night and significant daytime sleepiness, but the standard breathing-event score stays normal (often under 5). What distinguishes it is a high number of respiratory effort-related arousals, episodes where your brain wakes up briefly because of increased resistance in your airway, not a full blockage. Patients with this condition in one study averaged a sleepiness score of 15.3 on a scale where anything above 10 is considered excessive, despite having an average breathing-event score of just 2.3. It’s frequently misdiagnosed as simple snoring or unexplained hypersomnia.
Medical Conditions That Mimic Sleep Apnea Fatigue
Hypothyroidism is one of the most common medical reasons for persistent fatigue, and its symptoms overlap heavily with sleep apnea. An underactive thyroid causes muscle and joint pain, cold intolerance, and increased anxiety, all of which independently disrupt sleep quality. If your CPAP is working perfectly and you’re still exhausted, a simple blood test can rule this out.
Iron deficiency and anemia also cause fatigue that feels identical to untreated sleep apnea. Sleep specialists typically recommend screening for these conditions if you’ve been compliant with CPAP for six months without improvement. At that point, your care team will also likely screen for neurological conditions, anxiety, and depression, since all of these can keep you feeling tired no matter how well your airway is managed at night.
Medications That Add to Drowsiness
Some medications you take for other conditions can cause or worsen daytime sleepiness on their own. Benzodiazepines (commonly prescribed for anxiety), opioid pain medications, and antiepileptic drugs are well-known offenders. Antihistamines, muscle relaxants, and certain blood pressure medications can also contribute. If you started a new medication around the time your sleepiness worsened, or if you’ve been on one of these classes long-term, it’s worth discussing the timing with your prescriber. Sometimes switching to a different medication in the same class or adjusting when you take it can make a noticeable difference.
Prescription Options for Residual Sleepiness
For people who are genuinely compliant with CPAP, have good machine data, and have ruled out other causes, there are FDA-approved medications specifically for residual sleepiness in sleep apnea. Modafinil, armodafinil, and solriamfetol are all approved in the United States for this purpose. A large network meta-analysis of randomized trials confirmed that all three are effective at improving daytime alertness. These aren’t replacements for CPAP. They’re add-on treatments for the subset of people whose sleepiness persists despite good therapy.
Your sleep specialist is the right person to discuss these with, since the first step is always confirming that your CPAP is actually working as well as the data suggests and that no other treatable cause has been missed.