Terahertz time-domain spectroscopy (THz-TDS) is used to quantify and analyze the spectral characteristics of four gastrointestinal drugs: Enteritis capsules, Bismuth Citrate Potassium capsules, Rabeprazole Sodium enteric tablets, and Bifidobacterium Triptans capsules in the 0.25?2.40 THz band. Terahertz waves are sensitive to weak structural changes and can accurately identify drugs containing the same excipients. The experimental results show that the spectra of the four drugs are distinctly different; thus, THz-TDS technology cannot be used to identify drug components and classify drug effects. Additionally, there are evident differences in the spectral characteristics compared with those of the failed drugs manifested by the shift, addition, and disappearance of absorption peaks. The experimental study provides reference data for drug identification and efficacy identification by THz-TDS.