Background It has been suggested that inhibition of monoamine oxidase (MAO) activity by components of cigarette smoke may impact on smoking addiction, but it is unclear to what extent the known MAO inhibitors in tobacco smoke cause this inhibition.

Methods MAO inhibitory activity was measured in a series of tobacco particulate matter preparations from different brands of cigarette and loose-leaf tobacco commonly available in New Zealand.

Results When tobacco extracts were diluted to contain a physiologically relevant nicotine concentration of 0.2 μM, all samples tested inhibited MAO-A and MAO-B by between 4% and 12% in a standard assay. Per mg of nicotine, samples from factory-made cigarettes contained significantly less MAO inhibitory activity than did samples from loose-leaf tobacco. When inhibitory activity was calculated on a per mg of tar basis, there was no significant difference between loose-leaf tobaccos and factory-made cigarettes.

Conclusions The present study shows that the ratio of nicotine to MAO inhibitory activity varies depending on the type of tobacco product used. The roll-your-own tobaccos tested delivered more tar and more MAO inhibitory activity per mg of nicotine than the factory-made cigarettes. These findings suggest that smokers of roll-your-own tobacco may experience greater difficulty in stopping smoking.