The paper presents a novel non-destructive terahertz (THz) imaging technique for detecting and identifying illicit drugs hidden in mail envelopes. The method involves using a tunable THz-wave source to create multispectral transillumination images, which are then analyzed using component spatial pattern analysis to extract the spatial distributions of the drugs. The technique is demonstrated using methamphetamine, MDMA, and aspirin as samples, with the spatial patterns of each drug clearly distinguished. The authors show that their method can detect drugs at concentrations of ~20 mg/cm² and can be applied to mixtures of multiple drugs or layered arrangements. The technique has potential applications in drug screening, security, and pharmaceutical quality inspection.The paper presents a novel non-destructive terahertz (THz) imaging technique for detecting and identifying illicit drugs hidden in mail envelopes. The method involves using a tunable THz-wave source to create multispectral transillumination images, which are then analyzed using component spatial pattern analysis to extract the spatial distributions of the drugs. The technique is demonstrated using methamphetamine, MDMA, and aspirin as samples, with the spatial patterns of each drug clearly distinguished. The authors show that their method can detect drugs at concentrations of ~20 mg/cm² and can be applied to mixtures of multiple drugs or layered arrangements. The technique has potential applications in drug screening, security, and pharmaceutical quality inspection.