Vanillylmandelic acid has antioxidant activity, the IC ₅₀ value is determined as the amount of VMA required to reduce 50% of the starting concentration of free radical is 33*10 ^-6 M in the UV-Vis decolourisation DPPH assay.

Vanillylmandelic acid (intra-arterial injection over 1 min; 1, 10 and 100 mg/kg; the 60 min-observation period) produces a significant difference between vanillylmandelic acid groups and controls. Vanillylmandelic acid decreases the heart rate by 17.5%, 17.9% and 18.9% after 1, 10 and 100 mg/kg, respectively. Mean blood pressure is decreased by 13.5% in control animals as compared to 37%, 23% and 26% after 1, 10 and 100 mg/kg, respectively, in wistar rats.