Why Can't I Sleep? Common Causes of Insomnia

What counts as insomnia?

Everyone has occasional nights of poor sleep. Insomnia becomes a clinical concern when sleep difficulty: - Occurs at least three nights per week - Has lasted at least three months (chronic insomnia) or shorter (acute insomnia) - Causes real daytime consequences: fatigue, cognitive difficulty, mood problems, or reduced functioning

Insomnia is one of the most common health complaints in adults, affecting a substantial portion of the population. The American Academy of Sleep Medicine consensus supports targeting seven to nine hours of quality sleep per night for most adults 1Ref 1Watson NF, Badr MS, Belenky G, et al. (2015).Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society.Recommended sleep duration for adults; insufficient sleep raises health and functioning risks.

Psychological causes: stress, anxiety, and depression

Psychological factors are the most common drivers of both acute and chronic insomnia.

Acute stress activates the nervous system's alert response — the same one designed for survival threats. Racing thoughts, physical tension, and cortisol release all make sleep harder to reach and maintain. This is normal and usually resolves when the stressor resolves.

Chronic anxiety keeps the nervous system in a low-grade state of alert even in the absence of immediate threat. The mind rehearses worries at night, and the body remains too aroused to enter deep sleep. Generalized anxiety disorder is one of the most common co-occurring conditions with chronic insomnia 2Ref 2DeGeorge KC, Grover M, Streeter GS (2022).Generalized Anxiety Disorder and Panic Disorder in Adults.Anxiety disorders are among the most common co-occurring conditions with chronic insomnia.

Depression causes characteristic sleep disturbances — often waking too early in the morning, sometimes with difficulty falling asleep as well. Poor sleep in turn worsens mood, creating a reinforcing cycle. Treating depression improves sleep, and improving sleep supports mood recovery 3Ref 3O'Connor E, Henninger M, Perdue LA, et al. (2023).Screening for Depression and Suicide Risk in Adults: US Preventive Services Task Force Recommendation Statement.Depression causes characteristic sleep disturbances and bidirectional relationship with insomnia.

Conditioned arousal is a subtler but important mechanism: after weeks or months of poor sleep, many people develop an unconscious association between bed and wakefulness or anxiety. The bedroom itself becomes a trigger. This is a learned pattern, which is why behavioral treatment (CBT-I) is so effective at reversing it 4Ref 4Edinger JD, Arnedt JT, Bertisch SM, et al. (2021).Behavioral and Psychological Treatments for Chronic Insomnia Disorder in Adults: An American Academy of Sleep Medicine Clinical Practice Guideline.CBT-I is first-line treatment for conditioned arousal and chronic insomnia.

Behavioral and lifestyle causes

Many cases of insomnia are sustained by habits rather than caused by them — but habits can also be the initial trigger:

• Irregular sleep timing: Varying bedtime and wake time significantly disrupts the circadian rhythm. Social jet lag — sleeping late on weekends — is a common culprit.
• Excessive time in bed: Spending ten hours in bed when you can only sleep six creates fragmented, lighter sleep. This paradoxically worsens insomnia.
• Late caffeine: Caffeine has a half-life of roughly five to six hours. Afternoon coffee is still active at bedtime for most people 5Ref 5Drake C, Roehrs T, Shambroom J, Roth T (2013).Caffeine Effects on Sleep Taken 0, 3, or 6 Hours before Going to Bed.Caffeine consumed up to six hours before bedtime disrupts sleep quality.
• Screen exposure before bed: Evening light from screens suppresses melatonin and delays sleep onset 6Ref 6Chang AM, Aeschbach D, Duffy JF, Czeisler CA (2015).Evening Use of Light-Emitting eReaders Negatively Affects Sleep, Circadian Timing, and Next-Morning Alertness.Evening screen light suppresses melatonin and delays sleep onset.
• Alcohol use: Alcohol shortens time to sleep onset but fragments the second half of the night, reducing deep sleep 7Ref 7Ebrahim IO, Shapiro CM, Williams AJ, Fenwick PB (2013).Alcohol and Sleep I: Effects on Normal Sleep.Alcohol fragments the second half of the night and reduces deep sleep despite aiding initial onset.
• Daytime napping: Long or late naps reduce sleep drive and make nighttime sleep onset harder.

Medical conditions that cause or worsen insomnia

Several medical conditions directly interfere with sleep:

• Chronic pain: Any persistent pain condition — arthritis, fibromyalgia, back pain — raises arousal and interrupts sleep continuity
• Obstructive sleep apnea: Repeated breathing pauses fragment sleep, often without the person knowing. Daytime fatigue may be the main complaint.
• Restless legs syndrome: An urge to move the legs — typically worse at night and temporarily relieved by movement — can significantly delay sleep onset 8Ref 8Allen RP, Picchietti DL, Garcia-Borreguero D, et al. (2014).Restless Legs Syndrome/Willis-Ekbom Disease Diagnostic Criteria: Updated International Restless Legs Syndrome Study Group (IRLSSG) Consensus Criteria.Restless legs syndrome — the urge to move legs worsened at night — is a recognized cause of insomnia
• Hormonal changes: Menopause (hot flashes and night sweats), thyroid dysfunction, and other hormonal shifts disrupt sleep
• Frequent urination (nocturia): Waking to urinate is among the most common sleep disruptors in older adults, often driven by prostate enlargement, bladder overactivity, or heart failure
• Gastroesophageal reflux (GERD): Lying flat worsens reflux, causing discomfort that disrupts sleep

Medications and substances that interfere with sleep

Many common medications have sleep-disrupting effects as a side effect:

• Stimulants: ADHD medications (amphetamines, methylphenidate) taken late in the day
• Beta-blockers: Some suppress melatonin secretion
• Corticosteroids: Even short courses can cause insomnia
• Certain antidepressants: Activating SSRIs or SNRIs taken in the evening
• Decongestants: Pseudoephedrine in cold medications
• Nicotine: A stimulant that disrupts sleep continuity

Reviewing your medication list with a clinician is a useful early step if insomnia began after starting a new medication.

How do I figure out what is causing my insomnia?

A practical approach:

1. Keep a sleep diary for two weeks. Record bedtime, wake time, time to fall asleep, nighttime wakings, naps, caffeine, alcohol, medications, and next-day functioning. Patterns often emerge. 2. Review new medications. Did insomnia begin or worsen when you started something new? 3. Assess your mental health. Are anxiety or low mood prominent? These need direct treatment, not just sleep hygiene. 4. Consider whether you snore heavily or feel unrefreshed despite adequate time in bed. This pattern warrants a sleep study to evaluate for sleep apnea.

A Gale primary care clinician can review your history, assess for medical and psychiatric contributors, and guide the appropriate next step — whether that is a behavioral intervention, a referral, or an evaluation for an underlying condition.