A 30-year-old Japanese man with no previous psychiatric history presented to our facility with delusions, which had been ongoing for 2 months. Upon further interview, he confided that he had a past history of recurrent 5-methoxy-N,N-diisopropyltryptamine (5-MeO-DIPT or “Foxy”) abuse, as well as a recent history of recurrent ingestion of a legal aromatic liquid used as a recreational drug. After this episode, his condition improved and he did not follow up at subsequent appointments. However, 6 months later, he suffered a relapse of prolonged delusions after again ingesting a recreational aromatic liquid. An evaluation of the chronological sequence of the patient’s condition revealed that ingestion of these aromatic liquids, which can be purchased easily on the Internet, likely triggered the patient’s delusional episodes. We speculate that the patient’s recurrent abuse of 5-MeO-DIPT caused sensitization (or reverse tolerance), thus prolonging his delusions. Sensitization is the amplification of a response following repeated administrations of a stimulus. 5-MeO-DIPT is a popular drug of abuse, and it is highly probable that a large number of past 5-MeO-DIPT users are currently sensitized. This is an important latent factor underlying subsequent episode of drug-induced psychosis. Psychiatrists should consider the possibility of 5-MeO-DIPT sensitization when evaluating patients with acute psychoses.