Can ibs cause a drastic weight loss?

Check everything!: The GI tract has a very limited # of symptoms to signal its distress--nausea/vomiting, diarrhea/constipation, bloating, pain, fullness, bleeding, etc. As you know, many of these characterize IBS, but are also seen with inflammatory, infectious, ischemic, malabsorptive, & functional disorders. Involuntary weight loss obligates further evaluation & should not be ascribed to IBS alone.