 The most common side effect is diarrhea, sometimes severe. If it's severe, stop taking Linzess and call your doctor right away. Other side effects include gas, stomach area pain, and swelling. Talk to your doctor and learn more at Linzess.com or call 1-800-LIN-Z-E-S-S. Stop what you're doing and listen to this. Your God-given freedoms are up for the taking and those doing the taking.