TRICYCLICS AND WARFARIN AND OTHER ORAL ANTICOAGULANTS

Amitriptyline and possibly other tricyclics can cause unpredictable increases or decreases in prothrombin times, which can make stable anticoagulation difficult.
There is insufficient evidence to recommend an increased frequency of INR monitoring, but it would at least seem prudent to bear this interaction in mind when prescribing anticoagulants and tricyclics.