Psychological and Physiological Effects of Psilocybin

A study that investigated the psychological and physiological effects of psilocybin found there was “no cause for concern that [psilocybin]is hazardous with respect to somatic health” in healthy adults.

The study was published in 2004 in the scientific journal Psychopathology.

Participants for this study were recruited from university and hospital staff. All participants had to undergo a physical examination, blood analysis, and electrocardiogram to ensure that they were healthy. Participants who had personal or family history of mental disease or a previous history of drug use were excluded from the study. A total of eight male and female participants were recruited.

Those participating in the study received a very low, low, medium, and high dose of psilocybin and a placebo “in random order on five experimental days at least 2 weeks apart.”

150 to 300 minutes after ingestion of psilocybin (or placebo), the participants were administered the altered states of consciousness rating scale to assess changes in consciousness. The participants also completed the adjective mood rating scale and the Frankfurt attention inventory.

To assess the acute physiological changes produced by psilocybin, the participants heart rate was monitored for 24 hours starting 1 hour after ingestion. Blood pressure was also measured 30 minutes before psilocybin was administered and seven times afterwards. Finally, blood samples were taken before and after ingestion to assess the changes in blood chemistry and hormone levels.

Psychological Effects

At low, medium, and high doses of psilocybin, all participants reported changes in mood, sensory perception, time perception, and self. The authors noted that, “Typically, the experiences after [medium and high doses of psilocybin]were rated positive, with retrospective statements ranging from ‘pleasurable’ to ‘ineffably beautiful.’ ” One participant had a fearful experience after being given a high dose of psilocybin, but his anxiety was resolved without the need for pharmacological intervention.

All participants scored high on ratings of increased general inactivation, introversion, and dreaminess.

At very low and low doses of psilocybin,, no significant differences were found for the Frankfurt attention inventory compared to placebo. At medium and high doses, though, the scores were reduced by approximately 50%. According to the authors, this reduction in attention “may be confounded by the lack of motivation to perform well in this task.” The reduced attention at medium and high doses may represent the participants unwillingness to divert attention away from a novel experience.

Physiological Effects

High doses of psilocybin were found to cause a brief increase of blood pressure, but this change in blood pressure was not great enough to be considered dangerous in individuals with no cardiovascular condition.

Psilocybin also caused a small increase in levels of the hormones thyroid-stimulating-hormon (TSH), prolactin, cortisol, and adrenocorticotropic hormone, but hormone levels returned to normal after 300 minutes.

The authors concluded that psilocybin was not hazardous to healthy individuals, but that it should be avoided by those with cardiovascular problems. Psychologically, the authors found that psilocybin was “generally well tolerated and integrated by health subjects.”


Haslar, F., Grimberg, U., Benz, M.A., Huber, T. & Vollenweider, F.X. (2004) Acute psychological and physiological effects of psilocybin in healthy humans: a double-blind, placebo-controlled dose-effect study. Psychopharmacology, Vol 172: 145-156.

1 Comment

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    Lack of motivation to preform well in the test … so it turns us into cats is basically what you’re saying