Randomized, Double-Blind, Placebo-Controlled Trial of REL-1017 as Adjunctive Treatment for MDD

Inclusion Criteria:

• Body mass index (BMI) between 18.0 and 35.0 kg/m2.

• Diagnosed with Major Depressive Disorder (MDD) based on Structured ClinicalInterview for DSM-5 (SCID-5) for MDD.

• Inadequate response to 1 to 3 adequate antidepressant treatments in the current MDE.

Exclusion Criteria:

• Psychiatric hospitalization during the current major depressive episode.

• History or presence of clinically significant health conditions which in the opinionof the Investigator would negatively impact the safety of the participant.

• Participants who, in the Investigator's judgment, are at significant risk forsuicide.

• Pregnant or planning to become pregnant.