A member of the class of nitrosamines that is butan-1-ol substituted by a pyridin-3-yl group at position 1 and by a methyl(nitroso)amino group at position 4. It is a major metabolite of nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), which is a carcinogen found in tobacco and responsible for inducing lung cancer in smokers.