In addition to nicotine, cigarette smoke (tobacco) contains MAOIs. MAOIs were commonly prescribed as antidepressants and antipsychotics back in the 50s and 60s,

In addition to nicotine, cigarette smoke (tobacco) contains MAOIs. MAOIs were commonly prescribed as antidepressants and antipsychotics back in the 50s and 60s, but fell out of favor for various reasons, despite showing far greater efficacy than SSRIs. (one of these reasons was dietary: MAOIs have bad interactions with the amino acid "Tyramine", found in aged foods. However, Tyramine content in food has dropped dramatically since the 70s, and this is no longer a significant concern)