Increasing reports of anecdotal cases of acute adverse effects associated with the consumption of energy drink have been expressed by international bodies. This has necessitated the need to assess toxicological effects of Red Bull (RB) energy drink in this study. Eighteen adult rabbits were randomly divided into 3 groups of 6 rabbits (3 males and 3 females). Rabbits in groups 1, 2 and 3 (control) received daily oral doses of 23.1 ml RB, 11.5 ml RB and water respectively for 21 days. Venous samples were collected on days 1 (baseline), 14, 21 and 28, and animals were sacrificed on days 21 and 28. Biochemical assessment of liver and renal functions, and muscle activity were carried out by spectrophotometry, in addition to haematological and histological studies. Mortality of 11.1% was recorded, involving 2 female rabbits in group 1. For male rabbits in this group, significant increase (p<0.05) in total protein (TP) concentration and in activity of ALT and ALP occurred on days 14 and 21, with significant decrease in platelet counts. For female rabbits in group 2, significant increases in TP concentration and ALT activity were observed with significant decrease in albumin concentration and AST activity. Apart from slight increase in ALP activity of female rabbits, there were no significant differences in mean values of all rabbit parameters measured in the control group. Histology of rabbits in group 1 showed congestion and balloon degeneration of hepatocytes. This result showed that administration of RB to rabbits at doses lower than the manufacturer's recommended equivalent daily human intake of 500 ml caused adverse effects. There is need for caution in consumption of this drink.