Insomnia is a symptom of dozens of conditions, and roughly half of all insomnia cases seen in primary care are tied to another medical, psychiatric, or hormonal problem. While some people develop insomnia on its own, the majority of chronic cases trace back to something else going on in the body or mind. Understanding what might be driving your sleeplessness is the first step toward actually fixing it.
Depression and Anxiety
Mental health conditions are among the most common drivers of insomnia. About 90% of people with depression report some form of sleep disturbance, and insomnia is often the specific complaint. Among people already diagnosed with insomnia, 14 to 31% have major depression. The relationship runs deep: depression doesn’t just make you sad enough that you can’t sleep. It alters brain chemistry in ways that directly disrupt sleep architecture, particularly the rapid eye movement (REM) stage where dreaming and emotional processing happen.
Anxiety disorders are equally intertwined with insomnia. Between 24 and 36% of insomnia patients have an anxiety disorder, whether that’s generalized anxiety, panic disorder, PTSD, or a phobia. In one large population study, people at high risk for insomnia were nearly 10 times more likely to have anxiety and almost 20 times more likely to have depression compared to good sleepers. Interestingly, though, about half of people with insomnia in that study had neither anxiety nor depression, which points to how many other causes exist.
The Hyperarousal Connection
Many of the conditions linked to insomnia share a common thread: they keep your nervous system in a state of heightened alertness. Researchers call this hyperarousal, and it shows up as increased heart rate, elevated stress hormones, and overactive brain networks that refuse to quiet down at night. Your body’s stress system, which controls the release of cortisol, becomes overactive. Cortisol should drop to its lowest levels at night to let you relax into sleep. When stress, pain, or illness keeps that system firing, falling asleep feels nearly impossible.
On a brain level, people with insomnia show more fast-frequency electrical activity during sleep, essentially meaning their brain never fully powers down. The parts of the brain responsible for alertness and emotional reactivity stay too active relative to the networks that promote sleep. This is why insomnia so often accompanies conditions that involve chronic stress, pain, or emotional distress.
Hormonal and Endocrine Disorders
Your hormones play a direct role in sleep regulation, and when they’re out of balance, insomnia frequently follows. Hyperthyroidism, where the thyroid gland produces too much hormone, causes restlessness, anxiety, and a racing heart that can make sleep extremely difficult. Even hypothyroidism, the opposite problem, can paradoxically disrupt sleep despite causing daytime fatigue.
For women, menopause is one of the most recognizable hormonal triggers. As estrogen and progesterone levels decline, sleep quality often drops sharply. Progesterone in particular has a calming, sleep-promoting effect, so losing it can leave you wired at bedtime. Hot flashes and night sweats compound the problem by waking you repeatedly through the night.
Cortisol imbalances from conditions like Cushing’s syndrome or chronic stress can also keep you awake. If your body is producing too much cortisol at night, it overrides the natural signals that tell your brain it’s time to sleep.
Acid Reflux and Digestive Conditions
Gastroesophageal reflux disease (GERD) and insomnia have a well-documented relationship. When stomach acid flows backward into the esophagus, it causes heartburn, regurgitation, chest pain, and chronic coughing. These symptoms often worsen at night because lying down makes it easier for acid to travel upward. The discomfort wakes you repeatedly, and the anticipation of that discomfort can make it harder to fall asleep in the first place.
Researchers at Michigan Medicine have been studying this connection and note that it runs both directions: poor sleep can worsen reflux, and reflux disrupts sleep. Left untreated, chronic acid exposure can lead to changes in the esophageal tissue that carry more serious health risks, making this a particularly important cause of insomnia to identify and address.
Neurodegenerative Diseases
Insomnia and other sleep problems are common early features of Parkinson’s disease and Alzheimer’s disease, sometimes appearing years before the more recognizable symptoms. These diseases damage the specific brain regions that regulate your sleep-wake cycle and circadian rhythm, including networks in the brainstem and hypothalamus that act as your internal clock.
The relationship between neurodegeneration and sleep is particularly concerning because it appears to be a vicious cycle. During deep sleep, your brain activates a waste-clearance system that flushes out toxic proteins. Studies in mice show this system works about 60% more efficiently during sleep than during wakefulness. When sleep is disrupted, those harmful proteins accumulate faster. In Parkinson’s disease, sleep deprivation specifically increases levels of the protein that forms the toxic clumps characteristic of the disease. Poor sleep also triggers inflammation, damages the blood-brain barrier, and activates cell-death pathways, all of which accelerate neurodegeneration.
Other Sleep Disorders
Sometimes what feels like insomnia is actually caused by another sleep disorder operating underneath. Obstructive sleep apnea, where the airway repeatedly collapses during sleep, is frequently comorbid with insomnia. You may not realize your breathing is stopping dozens of times per night, but the repeated awakenings leave you feeling like you simply can’t stay asleep.
Restless legs syndrome is another common culprit. It creates an uncomfortable tingling or crawling sensation in the legs that worsens at rest and typically peaks in the evening or at bedtime. The urge to move your legs to relieve the sensation directly interferes with falling asleep and staying asleep. Both conditions are often comorbid with insomnia, and treating the underlying disorder usually improves the insomnia significantly.
Medications That Cause Insomnia
Insomnia is a recognized side effect of many common medications. Stimulant medications, including those prescribed for ADHD and narcolepsy, can disrupt sleep by keeping the brain in an alert state. Amphetamines are well known for this effect. Even newer wakefulness-promoting drugs list insomnia among their side effects.
Beyond stimulants, several other drug classes can interfere with sleep:
- Some antidepressants, particularly those with activating properties, can cause or worsen insomnia even though they’re sometimes prescribed for conditions that include insomnia as a symptom
- Beta-blockers used for blood pressure and heart conditions can suppress the hormone that regulates your sleep-wake cycle
- Corticosteroids prescribed for inflammation mimic cortisol and can keep your body in a wired, alert state
- Decongestants and some allergy medications have stimulant-like effects
If your insomnia started or worsened after beginning a new medication, that timing is worth noting and discussing with whoever prescribed it.
How Comorbid Insomnia Differs From Primary Insomnia
Clinically, insomnia is defined as difficulty falling asleep, staying asleep, or waking too early, at least three nights per week for three months or longer, with enough opportunity to sleep. When insomnia exists alongside another condition, it’s called comorbid insomnia, and it accounts for the majority of cases. Various studies suggest that nearly all insomnia patients seen in psychiatric settings, and about half of those in primary care, have an identifiable comorbid condition.
This distinction matters because treating only the insomnia without addressing the underlying cause often produces incomplete results. If acid reflux is waking you at 2 a.m., sleep hygiene tips alone won’t solve the problem. If an overactive thyroid is keeping your nervous system in overdrive, you need that treated before sleep can normalize. The comorbid insomnia model also explains why insomnia is so expensive to manage as a society, accounting for most of the estimated $30 to $35 billion in annual costs associated with chronic insomnia, precisely because it’s tangled up with so many other health problems.
The practical takeaway: if you’ve had insomnia for more than a few weeks, it’s worth looking beyond sleep itself. The insomnia may be your body’s loudest signal that something else needs attention.