More on Griffiths et al. 2017

Some thoughts on Griffiths et al. 2017, the new paper looking at effects of psilocybin coupled with spiritual practice on healthy study participants. See here for a summary the study results.

Reasons this study is exciting:

• Large effect sizes on a bigger sample. Griffiths et al. 2008 had 36 participants complete the study. Griffiths et al. 2017 had 75 participants complete, and found large increases in altruism, positive behavior change, and spirituality in the psilocybin groups (see Figure 5, p. 14).
• Unlikely to be a placebo effect. Griffiths et al. 2008 compared a high psilocybin dose to a active placebo of methylphenidate (Ritalin). Ritalin has a pretty different psychoactive profile than psilocybin, so study participants may have been able to determine which drug they were given, exposing them to expectancy effects. In contrast, the new study compared a very low dose of psilocybin (1 mg / 70 kg) to higher doses of psilocybin (20 and 30 mg / 70 kg). A very low dose of psilocybin has a similar (though much subtler) psychoactive profile to a high dose, so blinding was less likely to be broken than in previous studies.
• Not p-hacked. The study measured many variables; many of these showed significant differences between the low-dose and high-dose groups at p < 0.001 (see Table 5 on p. 13 and Table 6 on p. 15). All results were planned comparisons. Because of the number of p < 0.001 significant results, it's highly unlikely that the results were p-hacked.

And a couple notes of caution:

• No increase in Openness. MacLean et al. 2011, a follow-up to Griffiths et al. 2008, made waves by finding increases in psychological Openness 14 months after the psilocybin session. The new study followed a similar protocol, but did not find an increase in Openness at 6-month follow-up. The study authors didn't give a compelling reason for not finding an increase – from p. 15, "The failure to observe significant increases in Openness in the current study may be attributable to engagement in the program of spiritual practices or to some other aspect of the study design."
• No change in day-to-day spiritual practice. Griffiths et al. 2017 tested psilocybin administration alongside a regimen of spiritual practices (meditation, introspective journaling, etc.). Though the high-dose psilocybin groups experienced greater subjective spirituality, "The study did not provide evidence that psilocybin dose affected engagement with spiritual practices." (p. 13). So psilocybin administered in this format may not cause behavior change; the value of subjective assessments of experience relative to the value of concrete behavior changes is likely a disputed topic.