Phase III Long-term Extension Trial to Assess Safety and Efficacy of CYB003 in MDD (EXTEND)

Inclusion Criteria:

* Has successfully completed either CYB003-002 APPROACH or CYB003-003 EMBRACE and received both dose administrations of trial medication
* Has continued the same antidepressant medication at the stable dose/day throughout CYB003-002 APPROACH or CYB003-003 EMBRACE
* Has provided written informed consent, which includes compliance with the requirements and restrictions listed in the informed consent form
* Participants capable of producing sperm must use a condom plus spermicide (where publicly available) during the trial and for 12 weeks after their final dose of IP, if their partner is a person of childbearing potential. In addition, their partner of childbearing potential must continue to use a highly effective method of contraception (i.e., failure rate less than 1% when used consistently and correctly) throughout the trial until 12 weeks after the participant's final dose of IP
* Participants of childbearing potential (POCBP) who have a partner capable of producing sperm must agree to continue to use a highly effective method of contraception (i.e., failure rate of less than 1% when used consistently and correctly) in combination with the use of a condom plus spermicide (where publicly available) during the trial and for 12 weeks after their final dose of IP
* Female participants must have a negative pregnancy test at Baseline (the end of trial \[EOT\] Visit in the APPROACH or EMBRACE trial), and prior to dose administration on the dosing day

Exclusion Criteria:

* newly developed symptoms of schizophrenia spectrum or other psychotic disorders that manifested in the APPROACH or EMBRACE trial
* Significant suicide risk as defined by suicidal ideation as endorsed on items 4 or 5 on the C-SSRS at Baseline OR has experienced an adverse event (AE) of suicide ideation/attempt or self-harm in CYB003-002 APPROACH OR has had a \>1 point change in item 1 or 2 of the C-SSRS from Screening in CYB003-002 APPROACH
* Clinically relevant arrhythmia or vital sign changes noted during any of the dosing sessions in the APPROACH or EMBRACE trial
* Presence of clinically significant ECG abnormalities noted during the APPROACH or EMBRACE trials or at the Baseline of EXTEND
* Sensitivity or suspected sensitivity to CYB003 noted in the APPROACH or EMBRACE trial
* Positive urine test for drugs of abuse, or alcohol breath test prior to dosing.
* Unwilling to consent to audio and video recording of psychological support and dosing sessions