It is a spiritual endeavor. Neglecting this fact is why treatment of PTSD and other psychosocial disorders are often ineffective.

The use of psilocybin and mindfulness meditation both are in essence a spiritual quest which involves quieting the mind to decrease our sense of self in order to allow our larger sense of Self, which includes all of nature, to come to the forefront of our senses.  Below are are series of articles that point this out.

What is spirituality in relationship to our Western culture? This article in The Guardian puts that comparison in perspective. The articles highlights the views of Davi Kopenawa Yanomami, who has been dubbed the Dalai Lama of the Rainforest and is considered one of the most influential tribal leaders in Brazil.

#14Days: Psilocybin, where science meets spirituality (CBS News)
Psilocybin is a naturally occurring psychedelic compound found in some species of mushrooms that has been used in indigenous cultures as a spiritual sacrament for hundreds of years. Dr. Stephen Ross, director of the NYU Addiction Psychiatry Fellowship, believes this compound, administered in the proper dosage and in a controlled setting, may help resolve the symptoms of spiritual distress involved in a person with alcoholism.

Ceremonial PTSD therapies favored by Native American veterans
Eurekalert! 27 June 2014
The majority of survey takers felt that "most people who suffer from PTSD do not receive adequate treatment," said Urquhart. For Native veterans who did seek standard treatment, the results were often disappointing. Sixty percent of survey respondents who had attempted PTSD therapy reported "no improvement" or "very unsatisfied" (See also DOD and VA Can't Prove Their PTSD Care is Working, IOM Study Claims). Individual counseling reportedly had no impact on their PTSD or made the symptoms worse for 49 percent of participants. On the other hand, spiritual or religious guidance was seen as successful or highly successful by 72 percent of Native respondents. Animal assisted therapy – equine, canine, or other animals – was also highly endorsed.

The neuroscientific study of spiritual practices
Newberg AB. 
Front Psychol. 2014 Mar 18;5:215. 
PMID: 24672504
In considering the neuroscientific approach to religious and spiritual phenomena, one can ponder whether theological and epistemological issues can actually be addressed, sometimes referred to as “neurotheology” (Newberg, 2010). For example, brain correlates may help explain certain elements of spiritual practices. However, a biological correlate does not necessarily negate an actual spiritual component. Even situations in which religious states are induced by pharmacological agents does not necessarily detract from the spiritual nature of these states for the individual. For example, Shamanic practices in which various substances are ingested to aid in the spiritual journey are not viewed as less real or less spiritual by the participants because of the use of these exogenous substances.
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Below is a write-up in AL.com that features lead author Peter Hendricks, a professor of Clinical Psychology at the University of Alabama Birmingham regarding his article "Classic psychedelic use is associated with reduced psychological distress and suicidality in the United States adult population.":

Magic Mushrooms, LSD and other psychedelics might protect against depression and suicide

• Researchers culled the data from almost 200,000 responses to the National Survey on Drug Use and Health.
• People who said they used psychedelic drugs at least once in their life reported better mental health and fewer suicide attempts. 
• The results set psychedelics apart from other drugs. Lifetime users of substances such as cocaine, marijuana and heroin reported poorer mental health and a higher frequency of suicidal thoughts.
• After controlling for other variables, the research showed a strong correlation between use of psychedelics and better mental health.
• Hendricks said he thinks the improvement in mental health could come from the spiritual nature of the psychedelic experience.
• "Despite advances in mental health treatment, suicide rates have not declined," Hendricks said. "We have a problem with suicide and we don't seem to be getting better at preventing self-harm. It's exciting to think that this could be one of the interventions that could make a difference."
• Psychedelics could prove to be a one-time treatment with the possibility to change the lives of those suffering from mental illness.

Psilocybin-occasioned mystical experiences in the treatment of tobacco addiction

Garcia-Romeu A, Griffiths RR, Johnson MW.

Curr Drug Abuse Rev. 2014;7(3):157-64.

PMID: 25563443

Psilocybin-occasioned mystical experiences have been linked to persisting effects in healthy volunteers including positive changes in behavior, attitudes, and values, and increases in the personality domain of openness. In an open-label pilot-study of psilocybin-facilitated smoking addiction treatment, 15 smokers received 2 or 3 doses of psilocybin in the context of cognitive behavioral therapy (CBT) for smoking cessation. Twelve of 15 participants (80%) demonstrated biologically verified smoking abstinence at 6-month follow-up. Participants who were abstinent at 6 months (n=12) were compared to participants still smoking at 6 months (n=3) on measures of subjective effects of psilocybin. Abstainers scored significantly higher on a measure of psilocybin-occasioned mystical experience. No significant differences in general intensity of drug effects were found between groups, suggesting that mystical-type subjective effects, rather than overall intensity of drug effects, were responsible for smoking cessation. Nine of 15 participants (60%) met criteria for "complete" mystical experience. Smoking cessation outcomes were significantly correlated with measures of mystical experience on session days, as well as retrospective ratings of personal meaning and spiritual significance of psilocybin sessions. These results suggest a mediating role of mystical experience in psychedelic-facilitated addiction treatment.

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Psilocybin and spirituality: treatment for suicidal behavior, PTSD and moral injury
An October 2015 post motivated by a Veterans Affairs researcher advocating a spiritual approach to Veterans mental health issues such as PTSD, suicide, and moral injury.