This paper discusses the alternations in behaviour mechanisms of Pangasianodon hypophthalmus exposed to combiflam, a universally taken pain relief drug. Behaviour such as swimming, surfacing, aggressiveness, grouping and feeding were observed for dose concentrations increasing from 150mg to 2250 mg. The concentration of 450 mg showed a decrease in swimming speed and reduced appetite along with instances of fish surfacing for air. Fish are not seen swimming in groups anymore. The increase in dosage resulted in a sudden decrease and then increase in the swimming speed, whereas the other behaviours intensified with an increase in dosage concentration. This study gives an insight on the harmful effects of combiflam on fish behaviour.