Herbal medicine for insomnia: A systematic review and meta-analysis

Summary

Insomnia is a prevalent sleep disorder that can profoundly impact a person's health and wellbeing. Herbal medicine represents one of the most frequently used complementary and alternative treatments of insomnia. However, the safety and efficacy of herbal medicine for the treatment of this disorder is currently uncertain. In order to ascertain the evidence base for herbal medicine for insomnia, we systematically searched seventeen electronic databases and the reference lists of included studies for relevant randomised controlled trials (RCTs). Fourteen RCTs, involving a total of 1602 participants with insomnia, met the inclusion criteria. Four distinct orally administered herbal monopreparations were identified (i.e., valerian, chamomile, kava and wuling). There was no statistically significant difference between any herbal medicine and placebo, or any herbal medicine and active control, for any of the thirteen measures of clinical efficacy. As for safety, a similar or smaller number of adverse events per person were reported with kava, chamomile and wuling when compared with placebo. By contrast, a greater number of events per person were reported with valerian. While there is insufficient evidence to support the use of herbal medicine for insomnia, there is a clear need for further research in this area.

Introduction

Insomnia is a prevalent sleep disorder affecting up to forty percent of the population [1], [2], ∗[3], ∗[4], [5], ∗[6]. In many cases, insomnia presents as an isolated episode, often due to inadequate sleep hygiene or circadian rhythm disturbances [7]. It also can be a manifestation of an underlying medical disorder, psychiatric/behavioural disorder or medication usage [7], [8]. The social, economic, psychological and physical implications of insomnia are substantial, with evidence linking the condition to an increased risk of hypertension [9], cardiovascular disease [10], anxiety [11], and depression [12], [13], as well as impaired quality of life [14], work absenteeism, work-related accidents, poor work efficiency, and family dysfunction [15].

The treatment of insomnia varies. In most cases, sufferers do not seek medical treatment, and instead, adopt alternative measures such as reading, drinking alcohol or using non-prescription/over-the-counter drugs [4]. Some people may turn to prescribed medications to manage the condition, most commonly benzodiazepines and Z-drugs such as zolpidem and zopiclone. However, there are some concerns regarding the use of these medications, such as dependency [16]. Adverse events are also common. Benzodiazepines, for instance, can cause headaches, nightmares, daytime fatigue, nausea, confusion and falls [16]. The Z-drugs, which were expected to have advantages over benzodiazepines due to their different pharmacodynamic and pharmacokinetic properties, are associated with bizarre behaviours [17], as well as dizziness, falls, headaches and gastrointestinal upset [17]. These safety concerns limit the usefulness of these common hypnotic agents.

Concerns regarding the safety and effectiveness of these pharmaceutical agents, as well as a genuine interest in trying new therapies, may lead sufferers to seek out alternative treatments [18]. Holistic health-care beliefs, a need for active health-care participation, an increase in health-awareness behaviour, and to a lesser extent, dissatisfaction with Western medicine, may also motivate sufferers to pursue complementary and alternative medicines (CAM) over conventional treatments [45], [46], [47], [48].

Herbal medicine represents one of the most frequently used complementary/alternative treatments of insomnia. In a survey of 997 Quebec women [19], 18.5% reported the use of CAM to aid sleep, of which the herb chamomile was the most popular intervention used. Findings from the 2002 US National Health Interview Survey revealed 2.9% of insomnia sufferers in the US (which equates to 1.05 million users nationwide) used biologically-based therapies (which include herbal medicines) for the treatment of their condition [18]. Notwithstanding, the question arises as to whether herbal medicines are in fact a safe and effective treatment for insomnia.

Herbal medicine, which refers to the utilisation of plants or plant-derived materials for therapeutic purposes, has long been used by herbalists and indigenous communities to treat a range of sleep disorders; such plants include ashwaganda (Withania somnifera), hops (Humulus lupulus), lemon balm (Melissa officinalis), German chamomile (Matricaria recutita) and valerian (Valeriana officinalis) [20]. Empirical evidence indicates that several of these plants may assist in the management of insomnia by reducing sleep latency and improving sleep duration [21], possibly via interactions with glutamic acid decarboxylase [22] or via the modulation of gamma-amino butyric acid (GABA) and 5-hydroxytryptophan (5-HT) receptors [21]. This suggests that the use of herbal medicine as a treatment for insomnia is biologically plausible.

Many trials have examined the efficacy of herbal medicine for insomnia, but making sense of this literature requires a comprehensive and objective synthesis of the best available evidence. Even though a number of systematic reviews of CAM for insomnia have already been conducted [23], [40], [49], [50], these reviews have several limitations. First, the literature searches were conducted more than five years ago, and several pertinent studies have been published since then. Second, many relevant studies were overlooked in these reviews, which suggests that the search strategies employed were not entirely comprehensive. Some reviews were also narrative in nature, reported limited outcomes, or were either too broad or too narrow in scope. In light of these limitations, and the need to better understand the safety and efficacy of herbal medicine for insomnia, there is clear justification for conducting a more recent review in this area.