This paper reports a study of an absolute pitch possessor who, upon administration of the psychoactive drug Tegratol (carbamazepine), experienced a significant change in her pitch perception. The subject’s performance both in producing, as well as in identifying, random‐frequency tones was measured, covering the period of administration of the drug, as well as control periods before and after. The main effect of the drug was a downward shift of the perceived pitch as compared to the two control periods. The magnitude of the shift was observed to increase with increasing fundamental frequency of the stimulus; the average shift was about one semitone. Detailed results on the frequency dependence and time dependence of the pitch shifts are presented. This may be the first documented report of a significant, reversible change of pitch perception caused by a medication.