A new study found that AMITIZAâ„¢ (lubiprostone) may help relieve the symptoms associated with constipation-predominant irritable bowel syndrome (IBS-C). IBS is a condition that affects nearly 30 million people in North America and accounts for 25-50 percent of referrals to gastroenterologists. The study was presented today at Digestive Disease Week, the largest annual meeting of digestive disease specialists.