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Long-term safety and effectiveness study of CYB003 (deupsilocin besilate) with optional additional doses for people with Major Depressive Disorder

Fast replyInvestigationalNo 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 focuses on studying a medication called CYB003 for people with Major Depressive Disorder. The medication contains deupsilocin besilate and comes in capsule form that is taken by mouth. The study aims to examine how long the medication's benefits last after initial treatment and whether additional doses might help maintain its effectiveness.

The study is designed as a long-term extension trial, which means it continues to follow participants who have completed previous studies of the same medication. During the trial, participants may receive up to three additional doses of CYB003 while continuing their regular antidepressant medication. The maximum daily dose of the study medication is 16 milligrams, and the treatment period can last up to 43 days.

Throughout the study, researchers will monitor how well participants maintain their improvement in depression symptoms and how quickly symptoms might return, if at all. They will also track whether participants who didn't respond well to the initial treatment might benefit from additional doses. The study will evaluate both the safety of the medication and how well it works over a longer period.

The research process

The trial runs in 4 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial qualification

    You must have completed either the APPROACH or EMBRACE trial and received both doses of trial medication

    You need to maintain the same antidepressant medication at a stable dose that you took during the previous 12-week trial

    A pregnancy test will be required for female participants at baseline and before each dose administration

  2. Step 2

    Treatment requirements

    The medication (CYB003) will be given as oral capsules

    You may receive up to 3 additional doses during this extension trial

    You must refrain from nicotine use for up to 8 hours during dosing sessions

    If you are currently in psychotherapy, you must maintain the same frequency and setting throughout the trial

  3. Step 3

    Safety measures

    If you can produce sperm, you must use a condom plus spermicide during the trial and for 12 weeks after your final dose

    If you can become pregnant, you must use highly effective birth control during the trial and for 12 weeks after your final dose

    Your partner must also follow these contraception requirements if applicable

  4. Step 4

    Monitoring period

    Your depression symptoms will be regularly assessed using the MADRS (Montgomery-Åsberg Depression Rating Scale)

    The trial will monitor how long it takes before symptoms might return

    The study will track if you maintain improvement or need additional doses

    Regular evaluations will continue until the trial ends in September 2027

Who can join the trial?

9 criteria

  • Must have completed either the APPROACH or EMBRACE trial and received both doses of trial medication
  • Must have maintained the same antidepressant medication at a stable dose throughout the previous 12-week trial
  • If currently in therapy, must agree to continue with the same frequency and setting throughout the trial
  • Must be able to avoid using nicotine for up to 8 hours during dosing sessions
  • Male participants who can produce sperm must use both condom and spermicide if their partner can become pregnant, continuing for 12 weeks after the final dose
  • Female participants who can become pregnant must use highly effective birth control (with less than 1% failure rate) along with their partner using condom and spermicide, continuing for 12 weeks after the final dose
  • Female participants must have a negative pregnancy test at the start of the trial and before each dose
  • Women who may have entered menopause during the previous trial must continue following contraception requirements
  • Must provide written informed consent and agree to follow all study requirements

Who cannot join the trial?

15 criteria

  • Current diagnosis of any psychiatric disorder other than Major Depressive Disorder
  • History of substance abuse or dependence within the past 6 months
  • Significant risk of suicide as determined by clinical assessment
  • Presence of any unstable medical condition that could interfere with study participation
  • Previous failure to respond to three or more antidepressant treatments
  • Use of any investigational drug within 30 days before screening
  • Pregnant women or women planning pregnancy during the study period
  • Breastfeeding women
  • History of seizures or any other neurological disorder
  • Current use of medications that could interact with the study medication
  • Inability to comply with study procedures or visits
  • Any condition that, in the investigator's opinion, makes the patient unsuitable for the study
  • History of severe allergic reactions to medications
  • Abnormal laboratory test results that are clinically significant
  • Participation in another clinical trial within the past 30 days
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Investigated drugs

CYB003 is a novel psychedelic compound being studied for the treatment of major depressive disorder (MDD). The medication is designed to help people who experience symptoms of depression. It works by affecting certain brain pathways that regulate mood and emotional processing. This investigational therapy aims to provide longer-lasting relief from depressive symptoms compared to conventional antidepressant treatments.

What is already known about the treatment

CYB003 - A novel investigational drug currently undergoing Phase III clinical trials for the treatment of Major Depressive Disorder (MDD). This compound is being studied in a long-term extension trial to evaluate its safety profile and sustained therapeutic effects in patients with depression. While the specific molecular mechanism and administration form are not fully disclosed in the available trial data, the substance is being investigated for its potential antidepressant properties through a controlled, double-blind study design. The trial focuses on assessing the durability of treatment response, suggesting a potential role in managing persistent depressive symptoms.

Investigated diseases

Major Depressive Disorder - A common mental health condition characterized by persistent feelings of sadness, loss of interest in activities, and changes in daily functioning. The condition affects a person's thoughts, feelings, behavior, and physical well-being, often leading to difficulties with sleep, appetite, energy levels, and concentration. It typically involves periods of low mood lasting at least two weeks, during which normal daily activities become increasingly challenging. The disorder can develop gradually and may be triggered by life events, though sometimes it occurs without an obvious cause. MDD can affect people of any age and may involve cycles of better and worse periods.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2024-516805-22-00Protocol codeCYB003-004Estimated enrolment522 patientsSponsorCybin IRL Limited

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