What Causes Insomnia? 10 Reasons You Can't Sleep — and What to Do About It

Insomnia — the inability to fall asleep, stay asleep, or get restorative sleep — is one of the most common medical complaints in the world. An estimated 30% of adults experience occasional insomnia and 10% suffer from chronic insomnia that significantly impairs their daily functioning. Despite being so widespread, insomnia is frequently dismissed as stress or lifestyle, when in many cases it has identifiable, treatable underlying causes.

Understanding why you cannot sleep is the critical first step toward fixing it. Different causes require different solutions — and treating the wrong cause wastes months of time and often makes things worse.

This guide covers the 10 most common causes of insomnia in adults, how to recognise which one applies to you, and what treatments are available for each.

What is Insomnia?

Insomnia is defined as persistent difficulty with:

• Sleep onset

  taking more than 30 minutes to fall asleep

  
  

• Sleep maintenance

  waking during the night and having difficulty returning to sleep

  
  

• Early morning waking

  waking significantly before your intended time and being unable to sleep again

  
  

• Non-restorative sleep

  spending adequate time in bed but waking unrefreshed

Insomnia is classified as acute (lasting less than 3 months, often linked to a specific stressor or life event) or chronic (occurring at least 3 nights per week for 3 months or more, often with multiple contributing factors).

Chronic insomnia is a medical condition that warrants investigation and treatment — not simply a personality trait or something to push through.

Cause 1: Stress and Anxiety

The most common cause of insomnia across all age groups. Stress — whether from work, finances, relationships, health worries, or major life events — activates the hypothalamic-pituitary-adrenal (HPA) axis, raising cortisol levels in the evening when they should naturally be falling. Elevated evening cortisol suppresses melatonin production and keeps the brain in an alert, hypervigilant state incompatible with sleep.

Signs this is your cause:

• Difficulty falling asleep due to racing thoughts

• Mind replaying worries or problems when lying in bed

• Sleep improves during holidays or low-stress periods

What helps:

• Cognitive Behavioural Therapy for Insomnia (CBT-I) — the most evidence-based long-term treatment

• Structured wind-down routine — no work or stimulating content in the hour before bed

• Anxiety management — including therapy, mindfulness, and in some cases medication

  
  

Cause 2: Depression

Depression and insomnia have a bidirectional relationship — each worsens the other. Depression typically causes early morning waking (waking at 3–5am and being unable to return to sleep) rather than difficulty falling asleep, though both patterns occur. The neurochemical changes in depression — reduced serotonin, dopamine, and altered cortisol — directly disrupt sleep architecture.

Signs this is your cause:

• Characteristically waking very early and being unable to return to sleep

• Low mood, reduced motivation, and loss of pleasure accompanying the sleep problem

• Sleep improves when mood improves with treatment

What helps:

• Treatment of the underlying depression — antidepressants, therapy, or both

• Note: Many SSRIs can initially worsen insomnia — discuss timing of doses with your doctor

Cause 3: Poor Sleep Hygiene

Sleep hygiene refers to the habits, behaviours, and environment that support or undermine sleep. Many adults have developed chronically poor sleep habits — often without realising it — that directly cause insomnia.

Common sleep hygiene problems:

• Irregular sleep schedule

  going to bed and waking at different times each day confuses the circadian rhythm

  
  

• Screens in bed

  blue light from phones, tablets, and TVs suppresses melatonin production; the mental stimulation of social media and news activates the brain

  
  

• Caffeine too late

  caffeine has a half-life of 5–7 hours; a coffee at 3pm still has half its effect at 9pm

  
  

• Alcohol

  alcohol helps with sleep onset but significantly fragments sleep architecture in the second half of the night, causing early waking and poor quality sleep

  
  

• Long daytime naps

  napping for more than 20–30 minutes late in the day reduces sleep pressure at bedtime

  
  

• Using bed for work or screens

  weakens the brain's association between bed and sleep

What helps:

Consistent sleep and wake times (including weekends), no screens 60 minutes before bed, no caffeine after 2pm, keeping the bedroom cool and dark, and no alcohol within 3 hours of bedtime.

Cause 4: Obstructive Sleep Apnea (OSA)

Sleep apnea is a frequently undiagnosed cause of insomnia and non-restorative sleep. In OSA, the upper airway collapses repeatedly during sleep, causing brief awakenings (often without full consciousness) hundreds of times per night. The person wakes unrefreshed and often experiences excessive daytime sleepiness, morning headaches, and concentration problems.

Signs this is your cause:

• Loud snoring reported by a partner

• Waking with a dry mouth, sore throat, or headache

• Feeling unrefreshed regardless of hours slept

• Falling asleep involuntarily during the day

What helps:

• Sleep study (polysomnography or home sleep test) to confirm diagnosis

• CPAP (continuous positive airway pressure) therapy is the gold standard treatment

• Significant weight loss can resolve mild-to-moderate OSA in some patients

• Note: Modafinil is sometimes prescribed for residual daytime sleepiness in treated OSA patients — see our [Modafinil Guide]

Cause 5: Restless Legs Syndrome (RLS)

RLS causes uncomfortable sensations in the legs — often described as crawling, tingling, or an irresistible urge to move them — that occur primarily at rest and worsen in the evening. It directly prevents sleep onset and causes frequent night waking.

Signs this is your cause:

• Uncomfortable leg sensations that improve with movement

• Symptoms worst in the evening and at night

• Strong urge to walk, kick, or stretch the legs when trying to rest

What helps:

• Iron deficiency is a common underlying cause — blood test and iron supplementation if deficient

• Pregabalin and gabapentin are prescribed for symptom relief — see our [Pregabalin Guide]

• Dopamine agonists (pramipexole, ropinirole) are also commonly prescribed

  
  

Cause 6: Circadian Rhythm Disorders

The circadian rhythm is the body's internal 24-hour clock, regulated primarily by light exposure. Circadian disorders occur when the sleep-wake cycle is misaligned with the external environment.

Common types:

• Delayed Sleep Phase Syndrome (DSPS)**

  the body clock is shifted late; the person cannot fall asleep until 2–4am and sleeps late. Common in teenagers and young adults. People with DSPS are often labelled as having insomnia but actually have a timing disorder.

  
  

• Shift Work Disorder

  irregular work hours prevent alignment with the natural light-dark cycle

  
  

• Jet Lag

  transient circadian disruption from rapid time zone changes

What helps:

• Light therapy (bright light exposure in the morning) to advance a delayed body clock

• Melatonin at the correct time (not as a sleep aid, but as a circadian signal)

• For shift workers — Modafinil is FDA-approved for shift work sleep disorder

Cause 7: Medications That Cause Insomnia

Many commonly prescribed medicines have insomnia as a side effect:

Medicine Type	Examples	Sleep Effect
SSRIs / SNRIs	Fluoxetine, Sertraline, Venlafaxine	Difficulty falling asleep, vivid dreams
Beta-Blockers	Propranolol, Atenolol	Nightmares, early waking
Corticosteroids	Prednisolone, Dexamethasone	Difficulty falling asleep, racing thoughts
Stimulants	ADHD medications, some decongestants	Difficulty falling asleep
Diuretics	Furosemide, thiazide diuretics	Nocturia (waking during the night to urinate)
Thyroid Hormone	Levothyroxine (when dose is too high)	Difficulty falling asleep, palpitations

If insomnia began or worsened after starting a new medicine, discuss this with your doctor. Never stop a prescribed medicine without medical guidance — timing adjustments (taking a stimulating medicine earlier in the day) often resolve the problem.

Cause 8: Chronic Pain

Pain is a major disruptor of sleep. Conditions including back pain, arthritis, fibromyalgia, neuropathic pain, headache disorders, and any inflammatory condition can all cause insomnia by making comfortable sleep positions difficult and triggering arousals.

What helps:

• Optimising pain management — discuss with your doctor whether current pain control is adequate

• Pregabalin is specifically indicated for fibromyalgia and neuropathic pain and also has a sedating effect that can improve sleep in these conditions — see our [Pregabalin Guide]

• CBT-I has been adapted specifically for chronic pain-related insomnia

  
  

Cause 9: Menopause and Hormonal Changes

Hot flushes and night sweats are among the most disruptive causes of sleep disturbance in perimenopausal and menopausal women. The sudden rise in body temperature caused by a vasomotor flush disrupts sleep onset and causes repeated night wakings.

Additionally, the decline in oestrogen and progesterone directly alters sleep architecture — reducing deep (slow-wave) sleep and increasing sleep fragmentation.

What helps:

• Hormone replacement therapy (HRT) — effectively treats both hot flushes and the direct sleep effects of oestrogen deficiency

• CBT-I adapted for menopause-related insomnia

• Keeping the bedroom cool, lightweight bedding

Cause 10: Medical Conditions Causing Insomnia

Several underlying medical conditions directly impair sleep and should be investigated when insomnia persists without an obvious cause:

• Hyperthyroidism

  elevated thyroid hormone causes anxiety, elevated heart rate, and difficulty sleeping

  
  

• Gastro-oesophageal reflux disease (GERD)

  acid reflux worsens in the lying position, causing waking with heartburn or coughing

  
  

• Nocturia

  frequent need to urinate at night (from diabetes, enlarged prostate, diuretics, or kidney conditions) causes repeated awakening

  
  

• Asthma

  nocturnal asthma symptoms are common and cause sleep disruption

  
  

• Parkinson's disease and other neurological conditions

  directly alter sleep architecture

If insomnia is persistent, unexplained, and accompanied by other symptoms, a medical evaluation including thyroid function, blood glucose, and relevant investigations is appropriate.

When to Consider Prescription Sleep Medicine

When insomnia is persistent, significantly impairing quality of life, or has an identifiable cause that has been addressed without sleep improvement, prescription medicines may be appropriate as a short-term bridge:

• Zopiclone

  a non-benzodiazepine Z-drug effective for short-term insomnia (2–4 weeks maximum). See our [Zopiclone Complete Guide].

  
  

• Pregabalin

  particularly useful for insomnia driven by anxiety, neuropathic pain, restless legs, or fibromyalgia. See our [Pregabalin Guide].

  
  

• Modafinil

  for daytime sleepiness caused by shift work disorder or sleep apnea rather than nighttime insomnia. See our [Modafinil Guide].

All prescription sleep medicines require a valid prescription. At TheMedicineKart, we stock these medicines with USA-to-USA delivery in 4 business days. Email prescriptions to info@themedicinekart.com.

Frequently Asked Questions

How do I know what is causing my insomnia?

Keep a sleep diary for 2 weeks — recording bedtime, wake time, number of awakenings, estimated sleep quality, and any relevant factors (alcohol, stress, exercise, caffeine). This pattern often makes the cause clear. Share it with your doctor for assessment. If no cause is apparent, a medical evaluation is warranted to rule out sleep apnea, restless legs, thyroid disorders, and other conditions.

Is insomnia a symptom or a condition?

Both. Insomnia can be a symptom of an underlying condition (depression, sleep apnea, chronic pain) or a primary condition in its own right. Chronic primary insomnia — where the poor sleep has become self-perpetuating through anxiety about sleep, conditioned arousal in bed, and disrupted sleep pressure — is a distinct medical condition regardless of its original trigger.

Does alcohol help with sleep?

No — not overall. Alcohol helps with sleep onset (falling asleep faster) but significantly fragments sleep in the second half of the night by suppressing REM sleep and causing rebound arousal as blood alcohol levels fall. The net effect is reduced sleep quality, more night wakings, and feeling unrefreshed.

Is CBT-I better than sleeping tablets?

For long-term outcomes, yes. CBT-I (Cognitive Behavioural Therapy for Insomnia) produces durable improvements in sleep that persist after treatment ends. Sleeping tablets are more immediately effective but their benefit ends when the medicine is stopped — and they carry dependency risk with prolonged use. The combination of CBT-I and short-term medication has the best short and long-term outcomes.

When should I see a doctor about insomnia?

If insomnia has persisted for more than 4 weeks, is significantly affecting your work or daily life, is accompanied by other symptoms such as excessive daytime sleepiness, low mood, or physical symptoms, or if you have tried sleep hygiene improvements without benefit — consult your doctor.

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a licensed healthcare professional before starting any medication for insomnia or sleep disorders.