A paper I've read (Roche, 2010) gives a rather pessimistic view about the revelatory powers of hallucinogenics and suggests that they are rather detrimental to a rational worldview if used in the long-term. However the author also acknowledges that there is a correlation between intuitive thinking and the hallucinogenic experience. The paper draws on many sources and is very interesting to read.
A quote from Terrence McKenna who used LSD exuberantly..
So I did it and...there was a something, like a flower, like a chrysanthemum in orange and yellow that was sort of spinning, spinning, and then it was like I was pushed from behind and I fell through the chrysanthemum into another place that didn't seem like a state of mind, it seemed like another place. And what was going on in this place aside from the tastefully soffited indirect lighting, and the crawling geometric hallucinations along the domed walls, what was happening was that there were a lot of beings in there, what I call self-transforming machine elves. Sort of like jeweled basketballs all dribbling their way toward me. And if they'd had faces they would have been grinning, but they didn't have faces. And they assured me that they loved me and they told me not to be amazed; not to give way to astonishment.
— (McKenna, 1993)
Psilocybin has been studied to alleviate depression in cancer patients in a well-designed study (Griffiths et al. 2016). Excerpt from the abstract:
The effects of psilocybin were studied in 51 cancer patients with life-threatening diagnoses and symptoms of depression and/or anxiety. This randomized, double-blind, cross-over trial investigated the effects of a very low (placebo-like) dose (1 or 3 mg/70 kg) vs. a high dose (22 or 30 mg/70 kg) of psilocybin administered in counterbalanced sequence with 5 weeks between sessions and a 6-month follow-up. Instructions to participants and staff minimized expectancy effects. Participants, staff, and community observers rated participant moods, attitudes, and behaviors throughout the study. High-dose psilocybin produced large decreases in clinician- and self-rated measures of depressed mood and anxiety, along with increases in quality of life, life meaning, and optimism, and decreases in death anxiety. At 6-month follow-up, these changes were sustained, with about 80% of participants continuing to show clinically significant decreases in depressed mood and anxiety. Participants attributed improvements in attitudes about life/self, mood, relationships, and spirituality to the high-dose experience, with >80% endorsing moderately or greater increased well-being/life satisfaction.
Griffiths, R. R., Johnson, M. W., Carducci, M. A., Umbricht, A., Richards, W. A., Richards, B. D., ... & Klinedinst, M. A. (2016). Psilocybin produces substantial and sustained decreases in depression and anxiety in patients with life-threatening cancer: A randomized double-blind trial. Journal of psychopharmacology, 30(12), 1181-1197. doi: 10.1177/0269881116675513
McKenna, T. (1993). Alien Dreamtime [video].
Roche, G. T. (2010). Seeing Snakes: On Delusion, Knowledge, and the Drug Experience. In Dale Jacquette, ed. Cannabis Philosophy for Everyone: What Were We Just Talking About? Chapter 2, 35-49. Oxford: Blackwell. doi: 10.1002/9781444324440.ch2