Hyoscyamine
"I'm 18, female.
I seem to have drawn the short straw with this medicine. I'm very lightheaded, sensitive to light, and lethargic. On top of that, I've had headaches and dry-mouth, and I've lost my appetite. 
I suppose my symptoms have improved, but things are only better in the hours after taking the pill. Since I didn't have severe Irritable Bowel Syndrome, just cramping and frequent trips to the bathroom, the side effects negate the benefits. I cannot function as well as I would like. My lightheadedness has kept me from moving around much. I'll definitely be asking to have my dose lowered/the medication stopped, because I'd rather be in some pain than be on the verge of passing out whenever I stand."