The Effect of LSD on Neural Synchrony, Prosocial Behavior, and Relationship Quality

Inclusion Criteria:

* Written Informed Consent
* Understanding the procedures and the risks associated with the study.
* Age between 18 and 35 years old.
* Being in a steady relationship for at least 6 months.
* Proficient knowledge of the English language
* Previous experience with at least one psychedelic drug (psilocybin, LSD, mescaline, Ayahuasca, DMT, 5-MeO-DMT), but not within the past 3 months
* Absence of any major medical condition as determined by medical examination and laboratory analysis
* Absence of any major psychological condition as determined by medical examination
* Free from psychotropic medication
* Participants must be willing to refrain from taking illicit psychoactive substances during the study.
* Participants must be willing to drink only alcohol-free liquids and no coffee, black or green tea, or energy drink after midnight of the evening before the study session, as well as during the study day.
* Participants must be willing not to drive a traffic vehicle or to operate machines within 24 h after substance administration.
* Normal weight, body mass index (weight/height2) between 18 and 28 kg/m2

Exclusion Criteria:

* History of drug addiction (determined by the medical questionnaire, drug questionnaire and medical examination)
* Previous experience of serious side effects to psychedelic drugs (anxiety or panic attacks)
* Pregnancy or lactation
* Hypertension (diastolic \> 90 mmHg; systolic \> 140 mmHg)
* Current or history of psychiatric disorder (determined by the medical questionnaire and medical examination)
* Psychotic disorder in first-degree relatives
* Any chronic or acute medical condition
* History of cardiac dysfunctions (arrhythmia, ischemic heart disease,…)
* For women: no use of a reliable contraceptive
* Tobacco smoking (\>20 per day)
* Excessive drinking (\>20 alcoholic consumptions per week)
* Experience with a full dose of a psychedelic within the last three months
* Current use of SSRI medication