However, a growing consensus among researchers of smoking cessation have found nicotine replacement therapy (NRT) products to have limited effectiveness because tobacco users may be seeking the combination of MAO inhibitors (which are found in tobacco) and nicotine, or that NRT products do not deliver sufficient quantities of nicotine. MAO inhibitors in tobacco act to amplify the rewarding effects of nicotine, but may also act as a form of self-medication for people with depression. This could explain the association between mental illness and smoking, but a confounding variable is that chronic nicotine administration itself has been shown to desensitize nicotine receptors over time and lead to antidepressant effects. Smoking cessation itself is strongly associated with reduced depression, anxiety, and stress and improved positive mood and quality of life compared with continuing to smoke. It has been hypothesized that snus' success when compared with conventional NRT as a cigarette substitute could be attributed to its MAO inhibiting properties. However, studies seem to suggest that for MAO inhibition, tobacco has to be pyrolysized (i.e., ignited as in cigarettes, cigars, and pipes). The competing theory is that the success of snus as a smoking alternative is due to its ability to deliver nicotine similar to that acquired through cigarettes, and twice as high as that acquired through NRT. Furthermore, the use of snus, similar to cigarettes, offers a choice of brand, aesthetic rituals of use, and tastes of tobacco and thus has sensory effects that NRT products perhaps lack. The use of daily snus for smoking cessation has had a 54% success rate for complete abstinence, and a 60% success rate for great reduction in cigarette consumption.