The 2019 edition of this popular, pocket-sized reference book, written by the acknowledged experts in the field,  includes several hundred new drug-drug interactions and monographs. As in previous editions, the authors have included interactions that may produce clinically important adverse events based on their properties to assist in predicting interactions where limited data are available. The table of CYP450 and drug transporter substrates and modifiers now includes more than 565 drugs. In addition, many of the existing monographs have been revised to reflect newly published data. Interaction entries are easy to find in the index by either trade or generic name. The Horn and Hansten Drug Interaction Probability Scale is included to assess the probability of a causal relationship between a potential drug interaction and a patient event.