Many drugs have been implicated as causing acute pancreatitis (AP), mainly based on the recurrence of pancreatitis following rechallenge with a drug that the patient had been taking at the time of an initial episode of AP. However, estimates of the relative frequency with which drugs cause AP vary widely. This is largely because many patients may be taking a number of drugs, may have co-morbidities such as gallstone disease or hypertriglyceridemia, or may be consuming large amounts of alcohol, making it diffi cult to determine what actually is the primary cause of an episode of AP. Large, rigorously designed epidemdiological studies are needed to better defi ne the frequency with which the drugs in general cause AP and the specifi c risk of pancreatitis associated with any individual drug. Am J Gastroenterol 2011; 106:2189 -2191 doi: 10.1038/ajg.2011 Drugs have generally been considered to be a relatively uncommon cause of acute pancreatitis (AP), with an estimated incidence of 0.1 -2 % ( 1,2 ). However, a recent report of 170 cases of pancreatitis cared for at a single academic medical center in the Czech Republic concluded that drugs were the most likely cause in 5.3 % of cases, making drugs the third most frequent cause of AP aft er gallstones and alcohol ( 3 ). Another report, involving a retrospective review of 138 patients diagnosed with AP from a single center in France, attributed the etiology to drugs in 6.5 % of cases. However, the authors of this report qualifi ed this estimate by writing " Th is higher rate … must be examined with precaution due to the diffi culty in attributing causality " . ( 4 ).Indeed, it has not been easy to determine whether a specifi c drug is a cause of AP. More than 500 medications have been implicated, but most of the evidence comes from random case reports, with little in the way of sound epidemiological studies ( 5 ). When a case report describes a single exposure to a drug, no reliable conclusions can be made because case reports are oft en incomplete. Reports frequently do not even fully document a reliable diagnosis of AP and oft en have inadequate data regarding the drug dose and duration of treatment before the episode of AP and the extent of eff orts to exclude other common causes of AP. In addition, previous case reports and drug warnings from regulatory agencies may stimulate additional reporting because of heightened awareness of even the possibility a drug may cause AP. Also drugs that are widely used are more likely to be on the medication list of a patient with AP, regardless of the true cause; and new drugs are monitored much more closely for possible adverse eff ects than are medications which have been used for decades. As well stated in a recent review of drug-induced AP, " Th e incidence rates and relative risk of single drugs cannot be determined with the help of case reports alone " ( 2 ).However, one specifi c type of case report has been regarded as decisive in determining whether a drug is a likely cause of AP; i.e., a description of a well...