Johns Hopkins researchers report that a few longtime smokers quit after a carefully controlled and monitored use of psilocybin in the context of a cognitive behavioural therapy treatment program. The abstinence rate for study participants was 80 percent after six months. It is not that quitting smoking is a simple biological reaction to psilocybin, but more precisely when administered after careful preparation and in a therapeutic context, psilocybin can lead to deep reflection regarding one's life and spark motivation to change.
Not only is psilocybin being looked at carefully for smoking cessation, but as well, treating OCD/Eating Disorders, and Reducing anxiety and depression levels in Cancer patients. At the Heffter Zürich Research Center, a close examination of serotonin 5-HT2A neuroreceptor dynamics in the human brain following the administration of psilocybin, and its potential relevance for the treatment of obsessive-compulsive spectrum disorders (OCSDs), including OCD and eating disorders is under way. 
With CS Grob behind the helm, we have the first psychedelic treatment with terminally ill patients since the early 1970s. Grob and colleagues performed a pilot study of the effect of psilocybin on 12 patients with advanced-stage cancer and a diagnosis of acute stress disorder, generalized anxiety disorder, anxiety disorder due to cancer or adjustment disorder with anxiety.  Psilocybin did not cause any clinically significant adverse effects. It caused a significant decrease in anxiety, as assessed by the State-Trait Anxiety Inventory at one and three months after treatment, and improved mood, as measured by the Beck Depression Inventory after six months.  However, in a follow-up assessment at 8-16 months of 90 healthy people who received psilocybin in experimental studies, seven participants reported they had experienced negative changes in well-being due to the psilocybin. 
A lot of attention goes to treating cancer, but not treating the person dying from cancer. Psilocybin is being used to help the patient move into a positive mental state, thus these kinds of studies on an ethical level is sound, as they look to treat the whole human being.
1. Pilot study of the 5-HT2AR agonist psilocybin in the treatment of tobacco addiction.
3. Grob CS, Danforth AL, Chopra GS, et al. Pilot study of psilocybin treatment for anxiety in patients with advanced-stage cancer. Arch Gen Psychiatry. 2011;68:71–8.
4. Studerus E, Kometer M, Hasler F, et al. Acute, subacute and long-term subjective effects of psilocybin in healthy humans: a pooled analysis of experimental studies. J Psychopharmacol.