 Individual results may vary. Do not give to children less than 6, and it should not be given to children 6 to less than 18. It may harm them. Do not take Linzess if you have a bowel blockage. Get immediate help if you develop unusual or severe stomach pain, especially with bloody or black stools. 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 today. You may be able to save on Linzess and make fewer trips to the pharmacy.