A Study of a Deuterated Psilocin Analog (CYB003) in Humans With Major Depressive Disorder

The purpose of this study is to determine the efficacy, safety and tolerability of CYB003 compared to matching placebo as adjunctive treatment in patients with MDD.


Eligibility Criteria:
Inclusion Criteria:

* Participants must meet all the following criteria to be included in the trial:
* Age18 to 85 years.
* Participant has a diagnosis of MDD.
* Moderate to severe depression at Screening.
* Participants have been on a stable dose of antidepressant medication at an adequate dose in the last 4 weeks prior to Screening.
* Participant has a body mass index (BMI) of 40 kg/m2 or less (BMI ≤40 kg/m2), inclusive, at Screening.
* Participants with well controlled hypertension.
* Participant is able to refrain from smoking during the dosing session.
* Participants must use a condom plus spermicide during the trial and for 12 weeks afterwards.

Participants of childbearing potential must agree to use a highly effective method of and a negative pregnancy test at Screening and Day -1 prior to dosing.

* Participants of non-childbearing potential who are or were capable of producing eggs (ova) must have been postmenopausal or permanently sterile following hysterectomy, bilateral salpingectomy, or bilateral oophorectomy.
* Participants have provided written informed consent, which includes compliance with the requirements and restrictions listed in the informed consent form.

Exclusion Criteria

* Participants with any of the following characteristics/conditions will be excluded from trial participation:
* Current or previously diagnosed schizophrenia spectrum or other psychotic disorders.
* Family history of schizophrenia, schizoaffective disorder, or bipolar disorder type 1 (first-degree relatives).
* Significant suicide risk within 12 months of Screening.
* Current or previous diagnosis of treatment-resistant MDD.
* Has had electroconvulsive treatment, transcranial magnetic stimulation, deep brain stimulation, or vagal nerve stimulation for any episode of MDD in the last 6 months.
* Currently receiving a monoamine oxidase inhibitor, tricyclic antidepressants, mirtazapine, trazodone, moclobemide, buspirone, or an antipsychotic or mood stabilizer.
* Clinically relevant history of abnormal physical health interfering with the trial (including but not limited to, neurological, cardiovascular, respiratory, gastrointestinal \[including dyspepsia or gastroesophageal reflux disease\], hepatic, or renal disorder).
* Has hypothyroidism or hyperthyroidism, unless controlled on appropriate medication.
* Current diagnosis of uncontrolled hypertension or an arrhythmia, or clinically relevant abnormal results for heart rate.
* Participants have a presence or relevant history of organic brain disorders.
* Participant is taking or has taken OTC doses of 5 hydroxytryptophan or St John's Wort within prior to trial medication administration.
* Strenuous exercise prior to each clinic visit.
* Donation of blood or plasma within 4 weeks prior to first dosing and until 4 weeks after final dosing.
* Participants capable of producing sperm who will not abstain from sperm donation between first dosing and 12 weeks after final dosing.
* Participants of childbearing potential who are pregnant, breastfeeding, planning to conceive or unwilling to abstain from egg (ova) donation between first dosing and 12 weeks after final dosing.
* History of serotonin syndrome.
* Unwilling to consent to audio and video recording of psychological support and dosing sessions.