I checked for drug interaction between Synthroid (
levothyroxine) and nortriptyline, but there is only minor interaction reported.
However, a potentially life threatening condition called serotonin syndrome may occurred with nortriptyline, either taken alone or with MAOIs (or monoamine oxidase inhibitors) and/or other serotonergic drugs, such as triptans, tricyclic antidepressants, tramadol, and etc.