For past several weeks stools have been relatively thin/narrow, about twice the caliber of a pencil. coincided with beginning amitriptyline. no other symptoms. cause for concern?

Amitriptyline can cause constipation. So this change in bowel movements could be due to this medication. If you have a family history of colon cancer, or have noticed any blood in the stool, I would follow up with your primary doctor for further discussion and testing.

Although the medication can cause constipation, which could cause you to have narrow stools, it is important to contact your doctor immediately if you notice a change in your stool habits like this, because one potential symptom of colon cancer is narrow stools. Not saying that you have colon cancer, but saying that it needs to be evaluated. See your doctor or a G.I. doctor ASAP. Good luck.