Using natural supplementation as a treatment tool for mental health problems is becoming increasingly popular. Several studies using a multinutrient supplement called EMPowerplus (EMP+) have been conducted in humans with disorders such as Attention-Deficit/Hyperactivity Disorder (ADHD), but no studies have been conducted in animals or humans without disorders. Therefore, to address the gaps in the literature, the aim of this study was to assess the effects of EMP+ in a rat population on anxiety, aggression, and impulsivity which may be present in people who do not have a disorder. To investigate this, 40 male and 40 female rats were fed a diet consisting of 0%, 1.25%, 2.5% or 5% EMP+. They were tested during adolescence (PND 52-53) and again during mid-adulthood (PND 116-117) for anxiety and aggression, and during early adulthood (PND 92-96) and again during late adulthood (PND 127-130) for impulsivity. Due to the impact of the September 4th 2010 7.1 magnitude earthquake, data for some rats had to be excluded from anxiety and aggression analyses, leaving a sample size of 29 males and 34 females. Although there were no treatment main effects for any of the three behaviours, there were significant interaction effects between treatment and sex for measures of anxiety and aggression, showing that each sex reacted differently to the supplement. Male rats became less anxious, while female rats became more anxious. Of the five aggressive behaviours observed, significant interactions were found between treatment and sex for rough paw and allogrooming frequency. There were no significant effects involving treatment for impulsivity, but male rats were more impulsive when they were older (PND 127-130). Overall, the effects of EMP+ on the rats’ anxious, aggressive, and impulsive behaviours were mixed, and it is likely that the 7.1 magnitude earthquake and its subsequent aftershocks played a role in these results.