Abstract: The present invention provides a group of tobacco alkaloids, tobacco extract, Yerbamaté extract, and an extract of chewing gum and lozenges which are modulators of monoamine oxidase (MAO) activity (i.e., compounds and substances which inhibit MAO enzyme and prevent its biological activity). The MAO inhibitors of the present invention can cause an increase in the level of norepinephrine, dopamine, and serotonin in the brain and other tissues, and thus can cause a wide variety of pharmacological effects mediated by their effects on these compounds. The MAO inhibitors of the present invention are useful for a variety of therapeutic applications, such as the treatment of depression, disorders of attention and focus, mood and emotional disorders, Parkinson's disease, extrapyramidal disorders, hypertension, substance abuse, smoking substitution, anti-depression therapy, eating disorders, withdrawal syndromes, and the cessation of smoking.