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Study of deupsilocin besilate (CYB003) in adults with major depressive disorder comparing two doses against placebo

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What is this trial about?

A plain-language summary of the goals, design and what participants do

This clinical trial investigates a new treatment for Major Depressive Disorder, a serious mental health condition characterized by persistent feelings of sadness and loss of interest in daily activities. The study tests a medication called CYB003 (containing deupsilocin besilate) given as oral capsules, comparing it with placebo to evaluate its effectiveness in treating depression symptoms.

The purpose of this research is to assess how well two different doses of CYB003 work compared to placebo in treating adults with depression. The study medication will be given twice over a period of several weeks, with participants receiving either CYB003 capsules (8 mg or 16 mg) or placebo capsules. Throughout the study, participants will continue taking their current antidepressant medication.

During the trial, participants will attend multiple clinic visits where their depression symptoms will be evaluated using various assessment tools. The study will track changes in depression symptoms over 84 days to determine if the treatment is effective. The medication's safety will also be monitored throughout the study period.

The research process

The trial runs in 8 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial assessment

    Your eligibility for the trial will be confirmed through a detailed assessment of your major depressive disorder (MDD) symptoms

    A medical professional will verify your current antidepressant medication use and confirm that you have been on a stable dose for at least 4 weeks

    Your body mass index (BMI) must be 40 kg/m² or less

  2. Step 2

    First treatment day (Day -1)

    You will undergo baseline assessments and measurements

    If you are of childbearing potential, a pregnancy test will be conducted

  3. Step 3

    First dosing session (Day 1)

    You will receive either CYB003 capsules or a placebo capsule for oral use

    The dosing session will last up to 8 hours

    During this time, you must refrain from using nicotine

  4. Step 4

    First follow-up assessment (Day 2)

    Your response to the treatment will be evaluated

    Your depression symptoms will be measured using standardized assessments

  5. Step 5

    Second dosing session (Day 22)

    You will receive a second dose of either CYB003 or placebo

    The session will follow the same format as the first dosing session

  6. Step 6

    Second follow-up assessment (Day 23)

    Your response to the second treatment will be evaluated

  7. Step 7

    Assessment at Day 42

    A comprehensive evaluation of your depression symptoms will be conducted

    This is a key timepoint for measuring the treatment's effectiveness

  8. Step 8

    Final assessment (Day 84)

    Final evaluation of your response to the treatment

    Assessment of sustained improvement in depression symptoms

    Completion of quality of life questionnaires

Who can join the trial?

13 criteria

  • Age must be between 18 and 85 years at screening
  • Male participants who can produce sperm must use a condom with spermicide during the study and for 12 weeks after the last dose if their partner can become pregnant
  • Female participants who can become pregnant must use highly effective contraception during the study and for 12 weeks after the last dose, and have negative pregnancy tests before starting
  • Women who no longer have periods must be either post-menopausal (no periods for at least 12 months) or have had surgery to remove reproductive organs
  • Must provide written informed consent and agree to follow study requirements
  • Must have a diagnosis of Major Depressive Disorder (single episode lasting 4-24 months or recurring episodes) that first occurred before age 60
  • Depression must be moderate to severe, as measured by specific assessment tools
  • Depression symptoms must remain stable between screening and first day of study
  • Must be taking a stable dose of antidepressant medication for at least 4 weeks before screening, with inadequate improvement (less than 50% better)
  • If receiving counseling or therapy, it must be stable for at least 12 weeks before screening and remain unchanged during the study
  • Body Mass Index (BMI) must be 40 or less
  • Must be able to avoid using nicotine for up to 8 hours during dosing sessions
  • Must be registered with a healthcare professional who can confirm diagnosis and previous treatments

Who cannot join the trial?

14 criteria

  • History of resistance to antidepressant treatments or failure to respond to 3 or more adequate antidepressant treatments
  • Presence of other mental health conditions like bipolar disorder, schizophrenia, or severe personality disorders
  • Current substance abuse or dependence within the past 6 months
  • Significant risk of suicide or self-harm
  • Serious medical conditions that are not well-controlled
  • Pregnancy or breastfeeding
  • Use of certain medications that might interact with the study drug
  • Participation in another clinical trial within the past 30 days
  • History of seizures or other neurological disorders
  • Severe liver or kidney problems
  • Unstable heart conditions
  • History of allergic reactions to similar medications
  • Unable to comply with study procedures or follow-up visits
  • Cognitive impairment that could interfere with understanding study requirements
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Investigated drugs

CYB003 is an investigational medication being studied for the treatment of Major Depressive Disorder (MDD). It is being tested at two different dose levels to evaluate its effectiveness in treating depression symptoms. The medication is administered twice during the study to see how it affects people with depression compared to those who receive a placebo. This is an experimental treatment, and its full safety and effectiveness profile is still being evaluated through this clinical trial. The study aims to determine if this new medication can help reduce symptoms in adults who have Major Depressive Disorder.

What is already known about the treatment

CYB003 – An investigational medication being studied in clinical trials for the treatment of Major Depressive Disorder (MDD). This experimental drug is being evaluated in a Phase III clinical trial where participants receive two administrations of the medication compared to placebo. While the specific molecular mechanism is still under investigation, CYB003 is being developed as a potential therapeutic option for adults experiencing depressive symptoms. The study is being conducted as a multi-center, double-blind, randomized controlled trial to assess both the safety and effectiveness of this new treatment approach in managing depression. Note: Since there is limited publicly available information about CYB003 from the provided clinical trial data, this description focuses on the known aspects of the medication's current investigational status and intended use.

Investigated diseases

Major Depressive Disorder - A serious mood disorder characterized by persistent feelings of sadness, loss of interest in activities, and decreased energy that last for at least two weeks. The condition affects how a person thinks, feels, and handles daily activities, such as sleeping, eating, or working. People with this disorder often experience changes in appetite, difficulty sleeping or oversleeping, loss of energy, and difficulty concentrating. The disorder can also cause physical symptoms such as unexplained aches and pains. This condition can occur as a single episode or can be recurrent throughout a person's life.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2024-519270-40-00Protocol codeCYB003-003Estimated enrolment330 patientsSponsorCybin IRL Limited

sourced from the EU Clinical Trials Register and site verification

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