Negative mood, depression, irritability and aggression are known to occur in certain individuals due to paradoxical effect of g-amino butyric acid type A (GABA_A) receptor active compounds, e.g. alcohol, anabolic steroids and other neurosteroids, which constitutes a large problem in our society. Allopregnanolone (allo), a progesterone metabolite and neurosteroid, is found to enhance alcohol induced behaviour as well as being contributing factor to premenstrual disorder. The aim of this study was to develop an animal model, based on a scenario comparable to the social stress of patients negatively affected by (GABA_A) receptor active compounds, and optimize the model in terms of dose and interval between treatment and test. Male rats were housed in triads, within which they form stable hierarchies where the subordinate rat is weaker in competition which leads to stress and anxiety. In our model one smaller rat, assumed to be subordinate, was housed with two larger rats in order to heighten the effect of social competition. We found that in a 5 minutes' competition for sweetened milk, Milk Sugar Test (MST), the subordinate rat acquired low access to drink. However, after 0.5mg/kg and 1.0mg/kg allo treatment (i.v.), with a 5 minutes interval, the smaller rat showed dose dependant increase in drinking time linked to irritability behaviours. MST thereby constitutes a social competition model suitable for direct effects of GABA_A receptor active compounds and linked irritability behaviours. MST is also thought to display an animal scenario comparable to the situation of persons who experience paradoxical effects of GABA_A receptor active compounds.