Insomnia can be caused by many different things, including stress, underlying health conditions, and alcohol or drug misuse.

The causes of insomnia are discussed in more detail below.

Stress

Some people develop insomnia in response to a stressful event, and it continues even when the stress has been resolved. This is because they have become used to associating the sleeping environment with being alert.

Worrying about things, such as work and health, is likely to keep you awake at night. Worrying about not being able to fall asleep can also stop you from actually falling asleep, creating a 'vicious circle'.

Psychiatric problems

Underlying psychiatric problems can often affect a person's sleeping patterns. For example:

• mental health conditions – such as depression or bipolar disorder
• anxiety disorders – such as generalised anxiety, panic disorder or post-traumatic stress disorder
• psychotic disorders – such as schizophrenia

Health conditions

Insomnia can also be caused by underlying physical conditions including:

• heart disease 
• respiratory disease – such as chronic obstructive pulmonary disease or asthma
• neurological disease – such as Alzheimer's disease or Parkinson's disease
• hormonal problems – such as an overactive thyroid
• joint or muscle problems – such as arthritis
• problems with the genital or urinary organs – such as urinary incontinence or an enlarged prostate
• sleep disorders – such as restless legs syndrome, narcolepsy or sleep apnoea
• long-term pain

Alcohol and drug misuse

Drinking too much alcohol and taking drugs can affect a person's sleeping pattern.

Stimulants, such as nicotine and drinking too much caffeine (contained in tea, coffee and energy drinks) can also affect your sleep.

Medication

Some prescribed treatments or medicines available over-the-counter can cause insomnia. These include:

• antidepressants
• epilepsy medicine
• medication for high blood pressure (hypertension), such as beta-blockers
• hormone replacement therapy 
• non-steroidal anti-inflammatory drugs (NSAIDs)
• stimulant drugs, such as methylphenidate, which is often used to treat attention deficit hyperactivity disorder (ADHD) or modafinil, which is used to treat narcolepsy (a long-term sleep disorder that disrupts normal sleeping patterns)
• some medicines used to treat asthma, such as salbutamol, salmeterol and theophylline

Jet lag

A disturbed sleep pattern is one of the most common symptoms of jet lag.

After a long-haul flight, you may find it difficult to sleep at the correct times. For example, you may be awake at night and sleep during the day.