What causes insomnia: the difference between what starts it and what keeps it going

The single most useful framework for what causes insomnia is the behavioral model Arthur Spielman and colleagues set out in 1987, often called the 3P model. It separates three kinds of cause. Predisposing factors are the stable traits that make a person vulnerable: a tendency toward anxiety, a hyper-reactive stress system, an older age, or a family history. Precipitating factors are the events that trigger a bad stretch: a job loss, grief, pain, a new baby, a stressful deadline. Perpetuating factors are the behaviors and beliefs a person adopts to cope, which paradoxically keep insomnia going after the original trigger has faded. The power of the model is that it explains why almost everyone has a few bad nights but only some people develop lasting insomnia: the difference is usually not the trigger but what happens next.

Acute insomnia almost always has a precipitating cause, and stress is the most common one. Psychological stress raises arousal and pushes cortisol and heart rate up at exactly the wrong time, making the transition into sleep harder. Life changes that disrupt the schedule (a new shift, travel across time zones, a newborn) are common triggers, as are physical causes: pain, illness, a fever, breathing problems, restless legs, and hormonal shifts such as those around menopause. Medications and substances matter too; stimulants, some antidepressants, corticosteroids like prednisone, and decongestants can all provoke it. For acute insomnia the practical read is reassuring: identify the trigger, expect the sleep disruption to ease as it resolves, and avoid the coping habits that would otherwise make it stick.

The reason a few bad nights become a chronic problem is almost always the perpetuating layer, and this is the most important and least intuitive part. After a run of poor sleep, people do sensible-seeming things to catch up: they go to bed earlier, lie in later, nap in the afternoon, and spend long stretches lying awake in bed trying to force sleep. Every one of these backfires. Spending more time in bed than you can actually sleep dilutes sleep pressure and trains the brain to associate the bed with being awake and frustrated, which is the exact opposite of what you want. Anxiety about sleep then builds on itself, so the fear of not sleeping becomes its own cause. This is why chronic insomnia can persist long after the original stressor is gone, and why the treatment targets these habits rather than the trigger.

Some causes of insomnia are simply inputs that are set wrong, and they are the easiest to fix. Caffeine is the clearest: Christopher Drake and colleagues showed in 2013 in the Journal of Clinical Sleep Medicine that 400 mg of caffeine taken even 6 hours before bed measurably worsened sleep, which is why the safe habit is to stop caffeine in the early afternoon. Alcohol is the great false friend; it speeds sleep onset but fragments the second half of the night and suppresses REM, so a nightcap trades faster sleep for worse sleep later. An irregular schedule is a quieter cause: a wake time that drifts by hours across the week leaves the circadian clock unanchored, so tiredness arrives unpredictably. Bright evening light and screens delay the clock further. None of these are the deep cause of insomnia, but they load the dice against sleep and are worth clearing before anything else.

Insomnia frequently rides along with another condition, and treating the sleep in isolation then fails. Depression and anxiety disorders are the most common companions; the relationship runs both ways, so insomnia can be both a symptom and a driver of low mood. Chronic pain, an overactive thyroid, heart and lung disease, acid reflux, and hormonal changes all disturb sleep directly. Two sleep disorders in particular masquerade as insomnia: obstructive sleep apnea, where repeated breathing pauses fragment the night and leave a person feeling unrefreshed, and restless legs syndrome, where an urge to move the legs blocks sleep onset in the evening. The practical point is that insomnia which does not respond to the usual behavioral steps, or which comes with loud snoring, gasping, an unshakable low mood, or unexplained physical symptoms, deserves a medical assessment rather than another sleep aid.

Matching the fix to the layer is the whole game. For acute insomnia with a clear trigger, protect the basics and wait it out: hold a fixed wake time, get morning light, keep caffeine early, and resist the urge to catch up with naps and lie-ins, because that restraint is what stops it becoming chronic. For chronic insomnia, defined as trouble sleeping most nights for three months or more, the evidence-based first-line treatment is cognitive behavioral therapy for insomnia (CBT-I), which directly dismantles the perpetuating habits through stimulus control (the bed is for sleep only, get up if you cannot sleep) and sleep restriction (spend only as long in bed as you actually sleep, then expand). Charles Morin and colleagues showed in trials published in JAMA that CBT-I outperforms sleeping pills over the long run because it fixes the cause rather than masking it. Medication has a role for short bursts under a clinician, but it does not treat what keeps insomnia alive.