Insomnia is a disturbance of normal sleep patterns commonly characterised by difficulty in initiating sleep (sleep onset latency) and/or difficulty maintaining sleep (sleep maintenance). However, insomnia is highly subjective and although most healthy adults typically sleep between 7 and 9 hours per night, patterns vary greatly between people, and in any given person there are variations from night to night.
Insomnia can have a number of different causes: primary insomnia can be differentiated from insomnia associated with factors such as personal circumstances, physical or psychiatric comorbidities, concomitant drug treatments or substance abuse (drugs, nicotine, alcohol or caffeine). A 1996 World Health Organization survey indicated that 52% of people reporting a sleep problem had a well-defined mental health disorder and 54% reported a physical disorder.
The published estimates of the prevalence of insomnia vary from 10% to 38%. This variation can be attributed to the epidemiology surveys utilising different definitions, classification systems and diagnostic criteria. A recent systematic review of the epidemiological literature suggested that, while 30% to 48% of people reported the presence of insomnia symptoms and 8% to 18% reported dissatisfaction with sleep quality or quantity, only 6% met the criteria for a diagnosis of insomnia. Although 1 in 20 people are believed to present to healthcare professionals with insomnia-related symptoms, it is thought that many people with insomnia do not seek medical help.
The prevalence of insomnia has been reported to be higher in women and to increase with age. The age-related increase is believed to be multifactorial in origin and has been associated with changes in the time spent in different stages of sleep, increasing comorbidities, and lifestyle related factors.
Sleep disturbance and the resulting daytime fatigue cause distress and impairment of daytime functioning, both social and occupational, which have been associated with reduced quality of life. People with insomnia have been shown to have higher rates of mental health problems, drug and alcohol abuse, cardiac morbidity and healthcare utilisation, and to be at increased risk of accidents and overall mortality. However, it is difficult to differentiate the effects of insomnia from the effects of any associated factors, for example, comorbidities.
The electrophysiological parameters of sleep can be objectively assessed using polysomnography (PSG), which monitors sleep architecture by using electrodes applied to the scalp. However, insomnia is very subjective and there is great variation in sleep parameters both between individuals and in individuals on different nights. Therefore, although objective data on sleep parameters (for example, time taken to get to sleep, duration of sleep and number of awakenings) can be collected, such data are difficult to interpret and do not fully capture the impact of the condition. More subjective evaluations can be made using generic and disease-specific quality of life instruments and self-report measures such as sleep diaries and sleep quality indices.
The choice of management strategy for insomnia is dependent upon both the duration and nature of the presenting symptoms. Appropriate management of existing comorbidities may relieve the symptoms. The provision of advice on appropriate routines to encourage good sleep is fundamental to the overall management strategy, for example, avoiding stimulants and maintaining regular sleeping hours with a suitable environment for sleep. Other non-pharmacological interventions (for example, cognitive behavioural therapies) have also been shown to be effective in the management of persistent insomnia. However, although GPs and pharmacists can deliver appropriate advice and education, access to many non-pharmacological therapies is restricted through a combination of a lack of trained providers, cost and a poor understanding of available options.
A drug used to induce sleep is described as a 'hypnotic'. Although hypnotics can provide relief from the symptoms of insomnia, they do not treat any underlying cause. A number of hypnotic agents are licensed for the treatment of insomnia, including the benzodiazepines and zaleplon, zolpidem and zopiclone (Z-drugs).
It is difficult to ascertain how many prescriptions for hypnotics are written annually because benzodiazepines, which are commonly prescribed for insomnia, are also prescribed for other conditions. Up to 40% of people with insomnia self-medicate with hypnotics that are available without prescription from pharmacies (for example, sedative antihistamines).
Benzodiazepines are a group of structurally related compounds that enhance the effects of gamma-aminobutyric acid (GABA), which is the major inhibitory neurotransmitter in the central nervous system. The BNF 46th edition lists 6 benzodiazepines (nitrazepam, flunitrazepam, flurazepam, loprazolam, lormetazepam and temazepam) in section 4.1.1 on hypnotics. These agents are all available in generic form except for flunitrazepam and flurazepam, which are 'blacklisted' and cannot be prescribed within the NHS. A further 2 benzodiazepines, diazepam and lorazepam, are licensed for both insomnia and anxiety and are listed in the anxiolytic section of the BNF (section 4.1.2).
The effects of specific benzodiazepines are dependent upon the dose administered and the pharmacokinetic profile. Although there is variation between the estimates of elimination half-life, the BNF refers to loprazolam, lorazepam, lormetazepam and temazepam as having a shorter duration of action. Benzodiazepines with a longer elimination half-life (for example, diazepam and nitrazepam) tend to have prolonged effects and, if used as hypnotics, have a greater tendency to have next-day residual effects. This may affect mental function and cause psychomotor impairment, which can interfere with activities such as driving and working with machinery.
One of the key concerns about the use of benzodiazepines is that many people develop tolerance to their effects, gain little therapeutic benefit from chronic consumption, become dependent on them (both physically and psychologically), and suffer a withdrawal syndrome when they stop taking them. The withdrawal syndrome may be prolonged and may develop at any time up to 3 weeks after cessation of a long-acting benzodiazepine, or a few hours after cessation of a short-acting one. The syndrome includes anxiety, depression, nausea and perceptual changes. 'Rebound insomnia' also occurs and is characterised by a worsening of the original insomnia symptoms. There are also problems of abuse with benzodiazepines as they enhance and often prolong the 'high' obtained from other drugs and alleviate their withdrawal effects.
It has been estimated that 10% to 30% of chronic benzodiazepines users are physically dependent on them and 50% of all users suffer withdrawal symptoms. Factors potentially associated with an increased risk of developing dependency include short duration of action, long-term use, high dose, high potency, alcoholism and other drug dependency, personality disorders and use without medical supervision. The BNF notes that lorazepam is associated with a greater risk of withdrawal symptoms. The concerns over dependence led the Committee on Safety of Medicines to recommend that the use of benzodiazepines for the treatment of insomnia should be restricted to severe insomnia and that treatment should be at the lowest dose possible and not be continued beyond 4 weeks.