The molecular geometry of a major metabolite, C₁₄H₁₉NOS, of a potent anti-arrhythmic drug, 7-benzyl-3-thia-7-azabicyclo­[3.3.1]nonane (BRB-I-28), has been determined by X-ray diffraction. The 3,7-dihetero bicyclic system of the sulfoxide molecule adopts a chair–chair conformation like the HClO₄ salt of the BRB-I-28 molecule. The SN contact distance of 2.863 (2) Å in the present molecule is significantly shorter than that found in the crystal structure of its precursor [3.038 (4) Å]. The overall molecule possesses pseudo-mirror symmetry.