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A Randomized Controlled Trial of Cannabidiol vs Placebo Augmentation in Patients with First Episode Psychosis

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What is this trial about?

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

The study focuses on people who have experienced First Episode Psychosis, a condition where a person suddenly loses touch with reality and may see or hear things that are not there. Participants will continue taking their regular antipsychotic medication and will also receive either an oral dose of cannabidiol (often called CBD) or a placebo, which looks the same but contains no active ingredient.

The purpose of the trial is to see whether adding the study drug to standard treatment leads to greater overall improvement in symptoms after six weeks. Volunteers are assigned to one of the two groups by chance in a double‑blind manner, meaning neither the participants nor the study staff know who receives the active substance. Over the six‑week period, participants will attend regular visits where simple questionnaires and brief health checks are completed to track changes in mood, anxiety, daily functioning, and overall quality of life. After the treatment phase, participants will have a final follow‑up visit to assess any lasting effects.

The research process

The trial runs in 6 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Enrollment and baseline assessment

    After giving informed consent, you will attend an initial visit where a series of questionnaires and clinical scales are completed. these include a symptom rating called panss, a mood questionnaire, and quality‑of‑life measures. blood samples may be taken for future analysis. this visit establishes the baseline values that will be compared later.

  2. Step 2

    Random assignment to study medication

    Based on a computer‑generated random list, you will be assigned to receive either cannabidiol or a matching placebo. the assignment is double‑blind, meaning neither you nor the study staff will know which product you receive.

  3. Step 3

    Start of medication period

    You will begin taking one dose each day for a total of six weeks. the active product contains 1000 mg of cannabidiol taken by mouth (oral route). the placebo looks identical but contains no active substance. you will continue your regular antipsychotic medication throughout this period.

  4. Step 4

    Regular monitoring visits

    You will attend short clinic visits at week 2, week 4, and week 6. during each visit, safety checks such as blood pressure and heart rate are performed, and the same symptom questionnaires used at baseline are repeated. any side effects are recorded and reported.

  5. Step 5

    End of treatment assessment

    At the end of the six‑week period (week 6), a final set of assessments is completed. the change in the panss score from baseline is the primary measure of improvement. additional questionnaires on mood, anxiety, and quality of life are also collected.

  6. Step 6

    Optional long‑term follow‑up

    After the treatment period, you may be invited to return for additional assessments at later times to evaluate longer‑term outcomes. participation in these follow‑up visits is voluntary.

Who can join the trial?

10 criteria

  • Age 16 to 40 and able to sign a written consent form.
  • Currently taking an antipsychotic medication (a drug used to treat psychosis) for at least 3 weeks but no more than 16 weeks.
  • Taking at least the minimum dose recommended for first‑episode psychosis, and the doctor believes the medication is not working enough and that increasing the dose is not a good option.
  • Has a medication compliance score of 4 or higher on the Clinician Rating Scale (a tool doctors use to check how well a patient follows the medication schedule).
  • Meets the official DSM‑5 diagnostic criteria for schizophrenia, schizoaffective disorder, or schizophreniform disorder, confirmed with a structured interview called the SCID‑5‑RV.
  • Does not meet the modified Andreasen criteria for symptomatic remission (meaning symptoms have not fully gone away).
  • If able to become pregnant, must use a highly effective method of birth control (methods that fail less than 1% per year, such as hormonal pills, IUDs, implants, etc.) during the study and for 3 months after the last dose.
  • Willing and able to follow all study procedures and visits.
  • Agree to let their General Practitioner or specialist be informed about participation if required by local rules.
  • For those who choose to have the optional MRI scan, must be eligible for MRI (no metal implants, braces, or other contraindications).

Who cannot join the trial?

13 criteria

  • You have taken a different antipsychotic medicine (a drug used to treat psychosis) at a proper dose for at least four weeks before the study.
  • You are currently or have previously taken clozapine (a strong antipsychotic), sodium valproate (a mood‑stabilizer/ seizure medicine) or clobazam (an anti‑anxiety seizure medicine). You must be able to stop or switch these medicines before randomisation.
  • You are allergic (have hypersensitivity) to cannabidiol, sesame oil, sesame seed, or any other ingredient in the study drug.
  • You have serious liver problems, shown by liver enzyme (transaminase) levels more than twice the normal limit or bilirubin (a substance processed by the liver) more than 1.5 times normal.
  • You have had brain surgery or a neurological disorder such as epilepsy that could affect the study procedures.
  • Your IQ (intelligence quotient) is below 70, as measured by a standard IQ test.
  • You are pregnant or breastfeeding.
  • SCID‑5‑RV).
  • You have had active thoughts of suicide in the past two weeks, as measured by a questionnaire (CDSS) and judged unsafe by your doctor.
  • You meet the criteria for a substance use disorder (addiction) according to the DSM‑5, except for nicotine. Mild cannabis or alcohol use disorder is allowed only if you have not used cannabis more than three times a week in the last 30 days.
  • You participated in another clinical trial that used an experimental drug within the past three months.
  • You refuse any required safety checks, such as a urine pregnancy test (if you could become pregnant), blood tests, reporting side effects, or assessment of suicide risk.
  • You have any other serious illness or condition that the doctor believes would make participation risky or could affect the study results.
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Investigated drugs

  • Cannabidiol

    is a compound taken by mouth that comes from the cannabis plant but does not produce a “high.” In this study it is being tested to see if it can help reduce the overall symptoms of a first‑episode psychotic illness when added to the medicines participants are already taking. The drug is given as a liquid or tablet that the participant swallows each day for six weeks.

  • Antipsychotic medication

    refers to the standard drugs that people with psychosis already use to control symptoms such as hallucinations, delusions, and thought disturbances. In the trial, participants continue their usual antipsychotic treatment at the same dose they have been prescribed, and the study looks at whether adding cannabidiol provides any extra benefit.

What is already known about the treatment

CANNABIDIOL - This product is taken by mouth as a 1000 mg oral dose in a liquid or capsule form. Cannabidiol is a plant‑derived compound that is legally sold as a dietary supplement in many countries but is not yet approved as a prescription drug for psychosis, although it is studied in medical literature for several brain disorders. It is being tested mainly for use in people experiencing a first episode of psychosis, added to their regular antipsychotic medicines. At the molecular level it works by influencing the body’s endocannabinoid system, reducing activity at certain receptors and increasing the levels of natural signaling molecules, and it is classified as a phytocannabinoid with non‑psychoactive properties.

Investigated diseases

First-episode psychosis - A first episode of psychosis refers to the initial emergence of symptoms such as delusions, hallucinations, disorganized thinking, or abnormal behavior. It typically appears in late adolescence or early adulthood and may develop rapidly over days to weeks. Early signs often include subtle changes in perception, mood, or social functioning before full symptoms arise. As the episode progresses, symptoms can become more pronounced and affect daily life, communication, and relationships. The condition may fluctuate, with periods of worsening and partial improvement, and can evolve into a more chronic pattern if not addressed.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2025-521929-32-01Protocol codeSTEP-ENHANCEEstimated enrolment258 patientsSponsorUniversity Of Oxford

sourced from the EU Clinical Trials Register and site verification

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