The rings of the three-ring cytisine system in the title compound [systematic name: (1R,5S)-1,2,3,4,5,6-hexa-hydro-1,5-methano-8H-pyrido[1,2-a][1,5]diazo-cine-8-thione], C(12)H(16)N(2)S, have planar [maximum deviation 0.0170 (7) Å], half-chair and chair conformations. In the crystal structure, relatively short and directional C-H⋯π inter-actions and weaker secondary C-H⋯S contacts join the mol-ecules into helical chains along the [001] direction.