A drowsy patient with a positive purple urine test.

We report a pitfall in the investigation of amphetamine poisoning by urine test. A 21-year-old female who came to hospital with drowsiness and was reported to have positive purple urine test. This false positive urine test occurred as a result of drugs and substances of the same structure. Specific investigations were further recommended in order to detect the use of the amphetamines and allow appropriate treatment.