Anorexia nervosa is a serious illness and the treatments available to us have limited efficacy, so I welcome any news about new treatments. However, it is important to stress that the Peck et al. study is very early, very small, with no control group, and basically just wanted to find out whether psilocybin is a safe and tolerable treatment. The study also noted that four patients improved, but we do not know whether this was due to psilocybin, psychological support or simply by chance. For this reason, we should avoid getting our hopes up too high until there are larger, control group studies.

Psychedelics, including psilocybin, are a psychopharmacological treatment that is becoming fashionable and is being recommended to treat more and more mental problems. The logic behind this trend is confusing and contradictory and is reflected in this study: on the one hand, psilocybin is claimed to aid the psychotherapy process through the insights that the drug-induced experience can generate. On the other hand, it is claimed that it represents a specific medical treatment by correcting the neurotransmitter system of the brain.  

This study is representative of this trend and has very important limitations. It starts from an unproven hypothesis: that serotonergic function is impaired in people diagnosed with anorexia nervosa and that psilocybin may be effective because it acts specifically on this neurotransmitter system. The study is of very low quality, with a very small sample size of only ten patients and no control group. This research (like most of the research being done on psychedelics) does not pay attention to how the immediate psychoactive effects of the drugs impact on people's feelings and behaviour. This impact will inevitably influence symptom ratings and may produce the impression of improvement. It also overlooks the profound placebo effect that the hours of medical supervision and professional care associated with psychedelic treatment are likely to produce.   

As with other psychopharmacological treatments, psilocybin and the other psychedelics are becoming popular through the potent combination of financial interests and the desperation that mental suffering provokes in sufferers. However, their widespread clinical utility is unproven, and this study provides no new evidence for this, other than to contribute further to the popularisation of these substances.