Nicotine does not act alone in causing tobacco dependence and with monoamine oxidase inhibitors the most likely culprit, we took a closer look at the inhibitors in tobacco smoke. We discovered a monoamine oxidase inhibitor unlike any previously reported. Is this the chemical that works with nicotine to create dependence, and which is partly responsible for the positive effects of smoking on mood, which smokers report? We will complete the purification of this inhibitor, characterise it chemically and biochemically, and test its behavioural effect in an animal model of nicotine dependence to see if it is pharmacologically active. The knowledge generated will be important for better understanding tobacco dependence so that we can improve smoking cessation policies and practice. Smokers report that they self-medicate on tobacco, and knowledge of this chemical’s effects on mood may have implications for treatment of Parkinson's Disease, schizophrenia, anxiety and depression.