Dr.Klaassen's research interests have centered on how we adapt to chemicals in the environment.Studies have included the hepatobiliary disposition of xenobiotics,the toxicity of cadmium,the hepatotoxicity of chemicals,and mechanisms of chemical-induced thyroid tumors.He has published approximately 600 peer-reviewed articles,and more than 90 review articles and chapters for books.He was cited by Eugene Garfield in Current Contents(January 18,1993)as the scientist that had the fourth highest scientific impact in the United States in the study of xenobiotics(drugs and other chemicals),and in 2002 was named "Highly Cited Researcher"in Pharmacology(top 0.5%)by the Institute for Scientific Information.In 2007,InCites(Clarivate analysis) distinguished Dr.Klaassen as a "Most-Cited Researcher in Pharmacology and Toxicology"over the past 10 years and ranks him as the seventh most- cited researcher in Pharmacology and Toxicology in the world.Last but not least,according to Google Scholar,his publications have been cited more than 96,500 times and he has an h-index of 124