Role of the Serotonin 2A Receptor in Psilocybin-induced Altered States of Consciousness

Study Results

Results pending

The study team has not published outcome measurements, participant flow, or safety data for this trial yet. Check back later for updates.

Basic Information

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Recruitment Status

RECRUITING

Clinical Phase

PHASE1

Total Enrollment

16 participants

Study Classification

INTERVENTIONAL

Study Start Date

2025-04-21

Study Completion Date

2026-08-31

Brief Summary

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Psilocybin (active compound of "magic mushrooms") is a prototypical psychedelic substance that acts via agonism on serotonin (5-HT) 2A receptors. Psilocybin is rapidly metabolized into its active metabolite psilocin. Psilocybin is currently under investigation as potential treatment for various neuropsychiatric disorders. Psilocybin is also widely used for recreational purposes and as research tool in neuroscience. Besides its current clinical development, a clear characterization of the dose-response relationship of psilocybin is lacking. With the present study the investigators aim to close this knowledge gap by administering low (5mg) to high (40mg) single doses of psilocybin to healthy participants. Besides its agonism on 5-HT2A receptors, psilocin also binds to other receptors and inhibits serotonin transporters (SERT). To this data only few studies have investigated these effects and never at a high dose.

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Detailed Description

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Psilocybin is widely used for recreational and spiritual purposes. Additionally Psilocybin is currently reused in experimental studies with healthy subjects and in studies investigating its effects on patients suffering from anxiety, depression, addiction personality disorders and other pathological conditions.

The present PDR-study will characterize the subjective effects of different doses of psilocybin using modern psychometric instruments, explore the relationship between the plasma-concentration of psilocybin and its subjective effects, and examine the contribution of the 5-HT2A receptor in the psilocybin-induced alterations of consciousness in a mechanistic study in healthy subjects.

Participants will recieve doses of 5, 10, 20, and 40 mg psilocybin, 40 mg of psilocybin with pretreatment of 40 mg ketanserin, and placebo (control for psilocybin). Placebo pretreatment (control for ketanserin) will be used for all psilocybin administrations without ketanserin. Administrations will be separated by at least 10 days and are in random and counter-balanced order.

Conditions

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Healthy

Study Design

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Allocation Method

RANDOMIZED

Intervention Model

CROSSOVER

6-period random order, placebo-controlled, double-blind cross-over study

Primary Study Purpose

BASIC_SCIENCE

Blinding Strategy

TRIPLE

Participants Caregivers Investigators

Study Groups

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40mg Psilocybin plus 40mg Ketanserin

40mg Ketanserin oral followed by 40mg Psilocybin oral one hour later

Group Type EXPERIMENTAL

Ketanserin 40mg plus Psilocybin 40mg

Intervention Type DRUG

40mg Ketanserin oral will be administered followed by 40mg Psilocybin.

40mg Psilocybin

40mg Psilocybin oral

Group Type EXPERIMENTAL

40mg Psilocybin

Intervention Type DRUG

Placebo oral followed by 40mg Psilocybin one hour later.

20mg Psilocybin

20mg Psilocybin oral

Group Type EXPERIMENTAL

20mg Psilocybin

Intervention Type DRUG

Placebo oral followed by 20mg Psilocybin one hour later.

10mg Psilocybin

10mg Psilocybin oral

Group Type EXPERIMENTAL

10mg Psilocybin

Intervention Type DRUG

Placebo oral followed by 10mg Psilocybin oral one hour later.

5mg Psilocybin

5mg Psilocybin oral

Group Type EXPERIMENTAL

5mg Psilocybin

Intervention Type DRUG

Placebo oral followed by 5mg Psilocybin one hour later

Placebo

Placebo followed by Placebo

Group Type PLACEBO_COMPARATOR

Placebo

Intervention Type OTHER

Oral Placebo followed by oral Placebo one hour later

Interventions

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Ketanserin 40mg plus Psilocybin 40mg

40mg Ketanserin oral will be administered followed by 40mg Psilocybin.

Intervention Type DRUG

40mg Psilocybin

Placebo oral followed by 40mg Psilocybin one hour later.

Intervention Type DRUG

20mg Psilocybin

Placebo oral followed by 20mg Psilocybin one hour later.

Intervention Type DRUG

10mg Psilocybin

Placebo oral followed by 10mg Psilocybin oral one hour later.

Intervention Type DRUG

5mg Psilocybin

Placebo oral followed by 5mg Psilocybin one hour later

Intervention Type DRUG

Placebo

Oral Placebo followed by oral Placebo one hour later

Intervention Type OTHER

Eligibility Criteria

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Inclusion Criteria

1. Age between 25 and 75 years.
2. Sufficient understanding of the German language.
3. Understanding the procedures and the risks that are associated with the study.
4. Participants must be willing to adhere to the protocol and sign the consent form.
5. Participants must be willing to refrain from taking illicit psychoactive substances during the study (not including cannabis).
6. Participants must be willing not to drive a traffic vehicle or to operate machines within 48 h after substance administration.
7. Women of childbearing potential must be willing to use effective birth-control throughout study participation

Exclusion Criteria

1. Chronic or acute medical condition, including a history of seizures.
2. Body mass index 18-29.9 kg/m2
3. Current or previous major psychiatric disorder (e.g. psychotic disorders, mania / hypomania, anxiety disorders).
4. Psychotic or bipolar disorder in first-degree relatives, not including psychotic disorders secondary to an apparent medical reason, e.g., brain injury, dementia, or lesions of the brain.
5. Hypertension (SBP\>140/90 mmHg) or hypotension (SBP\<85 mmHg)
6. Psychedelic substance use (with the exception of cannabis) more than 20 times or any time within the previous two months
7. Pregnant or nursing women.
8. Participation in another clinical trial (currently or within the last 30 days).
9. Use of medications that may interfere with the effects of the study medications (any psychiatric medications and any medication with known to interact with the study substances).
10. Tobacco smoking (\>10 cigarettes/day).
11. Consumption of alcoholic drinks (\>15 drinks / week).
12. Body weight \< 45 kg.

Minimum Eligible Age

25 Years

Maximum Eligible Age

75 Years

Eligible Sex

ALL

Accepts Healthy Volunteers

Yes