A new review of published research has identified drugs for treating irritable bowel syndrome (IBS) with the fewest side effects. The researchers find that two commonly used drugs, rifaximin and lubiprostone, offer the best options for treating the widespread disorder that affects one in five Americans. They report the results of their systematic review and meta-analysis of 26 large trials in the April print issue of The American Journal of Medicine which is already available to read online. Lead author Dr. Mark Pimentel, director of Cedars-Sinai\'s Gastrointestinal Motility Program in Los Angeles, told the press: \"For the millions of patients who suffer from IBS, effective treatment options have been very scarce.\" IBS often occurs with pain or cramps in the abdomen, feeling of bloatedness and excess gas, and a visibly distended abdomen. Unfortunately, many available drug therapies for IBS come with just as unpleasant side effects, including insomnia, nausea, palpitations, and reduced appetite. For their study, Pimentel and colleagues reviewed common treatments for patients with IBS. They selected trials where participants had IBS with diarrhea or IBS with constipation, and were being treated with drugs recommended by the American College of Gastroenterology task force. For diarrhea forms of the condition, they evaluated three therapies: tricyclic antidepressants; alosetron, a drug that slows the progress of stool in the gut; and rifaximin, an antibiotic that stays in the gut. Rifaximin is currently approved by the US Food and Drug Administration as a treatment for traveler\'s diarrhea and hepatic encephalopathy. For constipation forms of IBS, Pimentel and colleagues evaluated serotonin reuptake inhibitors (a class of antidepressant), and lubiprostone, a drug that promotes gut secretion. They only included trials that described adverse events and where the number of patients who discontinued treatment because of adverse events were reported. In their analysis, they used the relative risk of experiencing an adverse event that meant having to stop using a drug, to calculate \"the number needed to harm\". The results showed some stark contrasts. For every 2.3 patients who derived a benefit from tricyclic antidepressants, one suffered side effects that were sufficiently severe to warrant stopping treatment. For alosetron, this ratio was 2.6 patients benefitting for every one who had to stop. But in the case of rifaximin, the ratio was 846 patients benefitting for every one who had to stop taking the drug. While lubiprostone and serotonin reuptake inhibitors showed a complete lack of \"harm\" for IBS patients with constipation. Pimentel said: \"We found that rifaximin and lubiprostone have the lowest level of harmful side effects of all the well-studied drug therapies for IBS.\" He said the findings underline the need to keep an eye on new therapies for IBS. \"While it is important to see benefit with drugs, harm is something we do not often assess well,\" he added. Pimental declared in interest in rifaximin, a drug that he discovered for the treatment of IBS. He consults for and sits on the scientific advisory board of Salix Pharmaceuticals Inc, who make the drug under license from Cedars-Sinai, the patent- holder. Funds for the study came from the Beatrice and Samuel A. Seaver Foundation.