A Mechanistic Study to Assess a Single Dose of CYB003 in Participants With Depression and Anxiety

Inclusion Criteria: * Participant is assigned female or male at birth. * Participant is aged between 21 to 65 years, inclusive, at Screening. * Participant has a BMI of 18 to 30 kg/m2, inclusive, at Screening. * Participant is ≥60 kg. * Participant has a diagnosis of MDD (as defined in the DSM-5 established through a clinician interview that includes the Mini-International Neuropsychiatric Interview) * Depression severity moderate to severe based on MADRS score ≥21. * Anxiety severity moderate to severe based on GAD-7 ≥10. * Inadequate response to current antidepressant medication in current episode of depression. * Participant has been on a stable dose (no more than 50% change) of antidepressant medication (SSRI or SNRI) in the last month prior to Screening. * Participants capable of producing sperm must use a condom during the trial and for 3 months after their dose of trial medication, if their partner is a person of childbearing potential. In addition, their partner of childbearing potential must use a highly effective method of contraception (i.e., failure rate less than 1% when used consistently and correctly) from dosing until 3 months following dosing. * Participants of childbearing potential must agree to use a highly effective method of contraception (i.e., failure rate less than 1% when used consistently and correctly) in combination with use of a condom by a partner who is capable of producing sperm, during the trial and for 3 months after dosing. Such participants must have a negative pregnancy test at Screening and Day 1. * Participants of non-childbearing potential who are or were capable of producing eggs (ova) must be postmenopausal or permanently sterile following hysterectomy, bilateral salpingectomy or bilateral oophorectomy. Postmenopausal is defined as spontaneous amenorrhea for at least 12 months, and a serum follicle stimulating hormone (FSH) level in the menopausal range, unless the participant is taking hormone replacement therapy or is using hormonal contraception. * Provision of giving written informed consent, which includes compliance with the requirements and restrictions listed in the consent form. Exclusion Criteria: * A reduction in the MADRS score of 25% or more between Screening and Baseline. * Failure to respond to \>2 antidepressant treatments given at an adequate dose for an adequate duration during the current episode of depression. * Current or previously diagnosis of schizophrenia spectrum or other psychotic disorders, including schizophrenia, schizoaffective disorder, schizotypal disorder, schizophreniform disorder or brief psychotic disorder; current or previous history of bipolar disorder, or current personality disorder (as determined by MINI at Screening). * Clinically significant risk of suicidality, as determined through a comprehensive psychiatric interview that incorporates the Columbia Suicide Severity Rating Scale (CSSRS); a score of 4 or higher on the suicidal ideation subscale of C-SSRS (past 6 months) or any suicidal behaviour (lifetime), would be exclusionary. * History of substance use disorder within the 12 months, as assessed by a structured clinical interview (Mini International Neuropsychiatric Interview \[MINI\], Version 7.0.2) or determined by self-report, or intake of \>21 units of alcohol weekly, and the inability to refrain from alcohol use from 48 hours before Screening and each scheduled visit until discharge from the study site. One unit is equivalent to a 285 mL glass of full-strength beer or 1 (30 mL) measure of spirits or 1 glass (100 mL) of wine. * Currently receiving a monoamine oxidase inhibitor, tricyclic antidepressant, other non-SSRI or non-SNRI antidepressants (e.g. bupropion, mirtazapine, etc), an antipsychotic or a mood stabilizer. * Exposure to psilocin, or any other psychedelics, such as ayahuasca, mescaline, LSD or peyote more than 10 times in the last 10 years, or any psychedelic use within 6 months prior to Screening. * Use of psychotropic medicine/supplement (or medicine/supplement that would interact with psilocybin) during the 28 days before dosing. Participants may take a stable chronic dose of antidepressant medication(s) and/or sedatives/hypnotics. The Investigator and study team may review medication on a case-by-case basis to determine if its use would compromise participant safety or interfere with study procedures or data interpretation. * Family history of schizophrenia or schizoaffective disorder (first degree relatives), or bipolar disorder type 1 (first degree relatives). * Clinically relevant history of abnormal physical health interfering with the study as determined by medical history and physical examinations obtained during Screening as judged by the Investigator (including but not limited to, neurological, endocrine, cardiovascular, respiratory, gastrointestinal \[including dyspepsia or gastroesophageal reflux disease\], hepatic, or renal disorder). * Participant has a presence or relevant history of any of the following medical conditions: organic brain disorders (e.g., epilepsy, seizure, intracranial hypertension, intracranial bleed and aneurysmal disease, brain tumor or other medical conditions associated with seizures or convulsions). * Diagnosis of hypertension or arrhythmia. * Clinically relevant abnormal heart rate (resting supine heart rate \>100 bpm) or blood pressure (resting supine systolic blood pressure (SBP) above 140 mmHg or diastolic blood pressure (DBP) above 90 mmHg) at screening. Screening supine SBP, DBP and heart rate for evaluation will be the average of 3 readings obtained after at least 5 minutes rest. Participants with abnormal vital signs which are out of range and deemed clinically significant by the Investigator at Day 1, following triplicate readings. * Presence of clinically significant ECG abnormalities at the Screening visit, as defined by medical judgement. * QT interval corrected for heart rate using Fridericia's formula (QTcF) \>450 msec at Scre