N-[3-(1,2,3,6-Tetrahydro-1-methyl-d3-4-pyridinyl)-1H-indol-5-yl]-2-thiophenecarboximidamide is the labeled analogue of N-[3-(1,2,3,6-Tetrahydro-1-methyl-4-pyridinyl)-1H-indol-5-yl]-2-thiophenecarboximidamide, a neuronal nitric oxide synthase(nNOS) inhibitor.