Which of the following narrow therapeutic index medications is federally classified as a controlled substance?

Carbamazepine is not classified as a controlled substance at the federal level. It is an anticonvulsant and mood stabilizer used to treat epilepsy and bipolar disorder, but it does not carry the same potential for abuse or dependence that leads to controlled substance classification.

Tacrolimus is an immunosuppressant used primarily in organ transplantation to prevent rejection. While it has a narrow therapeutic index requiring careful monitoring, it is not classified as a controlled substance due to its specific therapeutic use and low potential for abuse.

Argatroban is an anticoagulant used for the prevention and treatment of thrombosis in patients with heparin-induced thrombocytopenia. Like tacrolimus, it has a narrow therapeutic index but does not fall under the classification of controlled substances, reflecting its focused medical application without significant abuse potential.