Medicinal plants for insomnia: a review of their pharmacology, efficacy and tolerability

A number of medicinal plants are traditionally endowed with anxiolytic or sedative properties and, in the context of this revue, both indications are considered since the former may induce a mood conducive to the latter. For any sleep-inducing drug to be effective, a tranquil ambience needs to be established a priori. Thus, physical ailments (i.e. pain), factors interfering with sleep (i.e. noise), psychological conditions causing stress, psychiatric illnesses (i.e. depression) and other drugs that interfere with sleep (i.e. caffeine) need to be controlled, if possible. Kava-kava is a well-established hypnotic drug, with a rapid onset of effect, adequate duration of action and minimal morning after-effects. However, reports of serious hepatotoxicity with this preparation have led to it being banned in most countries worldwide. On the other hand, side-effects with valerian would appear to be bland indeed. However, it's slow onset of effect (2-3 weeks) renders it unsuitable for short-term use (i.e. 'jet-lag'), but it does have profound beneficial effects on sleep architecture (augments deep sleep) that may make it particularly suitable for long-term use and for the elderly. In a personal trial (not double-blind) in stress-induced insomnia, both kava and valerian improved sleep and the ill-effects of stress, and the combination of the two was even more effective for the control of insomnia. Aromatherapy (lavender, chamomile, Ylang-Ylang) would appear to improve sleep, but how practical a form of treatment this may be remains to be determined. The only other plant drug that may have some effect on sleep is melissa, but reports are too scanty to form any opinion about this. Based on animal experiments, passion flower (passiflora) may have a sedative action, but the sedative action of hops has not been investigated in any detail. In conclusion, there is a need for longer-term controlled studies with some of these compounds (particularly valerian). Aromatherapy constitutes a tantalising possibility. In the interpretation of this review, it should be borne in mind that the evidence on which it is based is often incomplete or missing, but that is all that is available. Consequently some conjecture on the part of the author is inevitable and should be appreciated as such.