Zelnorm has been pulled, as there is a small association with heart attacks when taking this IBS drug:

Swiss pharmaceutical maker Novartis AG will stop selling a drug to relieve constipation after it was linked to a higher chance of heart attack, stroke and worsening chest pain that can become a heart attack, federal health officials said Friday . . .

. . . Earlier this year, Novartis gave the FDA the results of 29 clinical studies of Zelnorm for treatment of a variety of gastrointestinal tract conditions. The analyses showed 13 of 11,614 patients given Zelnorm had serious and life-threatening cardiovascular side effects, while just one of the 7,031 patients given dummy pills did, the FDA and Novartis said in separate statements.