The effects of lavandula angustifolia on animal and human laboratory models of anxiety

Lavender (Lavandula angustifolia) is a popular treatment for stress and mild anxiety. Currently, there are few reliable investigations of its efficacy because cognitive and associative effects of odours can confound pharmacological effects. Some of these problems can be overcome by testing the effects of odours in animals, and by using orally-administered lavender in sealed capsules in human participants. In addition, a criticism of current studies is that most employ short-term administration of lavender, even though humans most often use lavender over longer time-periods. There are two parts to this thesis. The first part addressed two questions; whether lavender odour exhibits anxiolytic effects in animal models of anxiety, and whether chronically administered lavender is more effective than acutely administered lavender. The second part addressed the question of whether, in a randomised double-blind placebo-controlled trial, orally-administered lavender exhibits anxiolytic effects in humans. This thesis makes three significant contributions: First, these studies provided a validation of the gerbil elevated plus-maze model of anxiety in both male and female gerbils, a model that has only previously been validated in female gerbils (Varty et al., 2002). Second, the studies on gerbils have shown that both lavender and rose essential oils have anxiolytic effects, which, rather than dissipating following acute odour administration (Cooke & Ernst, 2000), potentiate over time. Lavender’s effects were particularly apparent in female gerbils on measures related to risk-assessment, a behaviour that has been related to the human anxiety trait of worry (Blanchard, Blanchard, Griebel, & Nutt, 2008). Third, lavender had a clear dose response effect in reducing baseline anxiety in humans when tested acutely via oral administration, although there were no effects when more severe anxiety was induced. The route of administration and the fact that iv lavender had dose response effects indicate that lavender’s effects are not caused by psychological qualities of the odour, but are more likely to be due to direct pharmacological effects. Again, and comparable to results in gerbils, lavender’s anxiolytic effects in human females were more noticeable, particularly during the anxiety task and in the recovery phase of the study. In summary, prolonged exposure to lavender odour relieved anxiety in a validated animal model of anxiety, and orally-administered lavender alleviated mild anxiety in humans. In both cases, results were more prevalent in females