Not yet recruitingPHASE3INTERVENTIONAL

Stratification and Treatment in Early Psychosis Study -ASSIST

The ASSIST study is investigating a new approach for people with psychosis that hasn't fully responded to clozapine, a standard medication. We want to see if adding cannabidiol (CBD), a component of cannabis (but without the 'high'), can improve how clozapine works and if it's safe to use. Half the participants will receive CBD, and the other half a dummy pill, alongside their usual clozapine. This is a large, international study involving many centres. We'll be carefully monitoring symptoms and looking for clues in blood and stool samples, and brain scans, to understand why some people respond better than others. The goal is to find better ways to help people living with psychosis.

At a glance

Status

Not yet recruiting

Phase

PHASE3

Sponsor

University of Oxford

Enrolment target

250

Start

01 Jun 2026

Estimated completion

01 Sep 2029

Treatment Resistant Psychosis Psychosis

What is this study about?

This study, called ASSIST, is looking for better ways to help people who have psychosis that hasn't fully improved with their current treatment, specifically with a medicine called clozapine. Psychosis is a mental health condition where someone might experience things like hallucinations (seeing or hearing things that aren't there) or delusions (strong beliefs that aren't based in reality). Clozapine is often used when other treatments haven't worked well enough.

The main aim of this study is to see if adding a substance called cannabidiol, or CBD, to clozapine can make the treatment more effective. CBD comes from the cannabis plant but doesn't cause the 'high' associated with cannabis. We also want to confirm that CBD is safe for people with psychosis.

Participants will be placed into one of two groups by chance (like flipping a coin). One group will receive CBD, and the other will get a 'placebo' (a dummy pill that looks like CBD but contains no active medicine). No one, not even the doctors, will know who is getting what until the end of the study. This helps us get fair results. Everyone in the study will continue to take their clozapine as usual. Over 12 weeks, we'll carefully watch how participants are doing and collect information to see if CBD makes a difference.

Key takeaways

This study is for people with psychosis that hasn't fully improved with clozapine.
It's testing if adding CBD can improve clozapine's effectiveness and safety.
Participants will receive either CBD or a dummy pill, plus their usual clozapine.
The study involves regular clinic visits and health checks over 12 weeks.
Your participation is voluntary, and you can withdraw at any time.

Who may be eligible?

To join this study, you need to be between 16 and 50 years old. You should have been diagnosed with schizophrenia, schizoaffective disorder, or schizophreniform disorder, and have started antipsychotic treatment for psychosis within the last 10 years.

You also need to be taking clozapine for at least 8 weeks, and it should be clear that your psychosis symptoms haven't fully gone away. We'll check the level of clozapine in your blood to make sure it's at a certain amount for the study.

If you're able to have children, you'll need to agree to use effective contraception during the study. You should also be willing and able to follow all the study's instructions. If you're interested in the optional brain scans, you'll need to be suitable for an MRI, for example, not having certain types of metal implants.

Could this study suit you?

Answer these quick questions to see if you may be eligible. This is a guide only — the research team makes the final call.

Are you between 16 and 50 years old?
Have you been diagnosed with schizophrenia, schizoaffective disorder, or schizophreniform disorder?
Have you been taking clozapine for at least 8 weeks, and it hasn't fully worked for your symptoms?
Are you willing to attend regular clinic appointments and follow study instructions?
If you can have children, are you willing to use effective contraception during the study?

Answer every question to see your result.

What does participation involve?

If you decide to take part in this study, you'll first have a screening visit to check if you meet all the requirements. If you do, you'll be randomly assigned to either receive CBD or a placebo (dummy pill), alongside your regular clozapine medication, for 12 weeks. Neither you nor your study doctor will know which one you're receiving.

During these 12 weeks, you'll have regular visits to the clinic. At these visits, doctors and nurses will assess your symptoms, check your overall health, and ask about any side effects. You'll likely have blood tests and provide other samples, such as stool samples. You might also be invited to have optional brain scans (MRI).

The total duration of your active participation will be 12 weeks, plus the initial screening period. There might be some follow-up contact after the treatment period to see how you're doing. All this will be explained in detail before you decide to join.

Potential risks and benefits

Taking part in a study like this might have potential benefits, such as receiving extra medical attention and having the chance to try a new treatment that might help your symptoms. However, there's no guarantee that you will personally benefit. Potential risks include experiencing side effects from the study medication (CBD or placebo), which will be carefully monitored. You will also need to attend several clinic visits and undergo various assessments, which might involve some inconvenience. It's very important to remember that participating is entirely your choice, and you can withdraw from the study at any time, for any reason, without it affecting your usual medical care.

Locations (15)

Some site locations are approximate. We're improving this — please verify with the trial team before travelling.

Charité Universitätsmedizin
Verified postcode
Berlin, Germany
University Hospital Cologne
Verified postcode
Cologne, Germany
Ludwig-Maximilian-University Munich
Verified postcode
Munich, Germany
National and Kapodistrian University of Athens
Verified postcode
Athens, Greece
Shalvata Mental Health Center
Verified postcode
Hod HaSharon, Israel
Geha Mental Health Center
Verified postcode
Petah Tikva, Israel
Sheba Medical Centre
Verified postcode
Ramat Gan, Israel
University of Campania 'Luigi Vanvitelli'
Verified postcode
Naples, Italy
Stichting Amsterdam UMC
Verified postcode
Amsterdam, Netherlands
Hospital General Universitario Gregorio Marañón
Verified postcode
Madrid, Spain
Hospital Universitario Virgen del Rocío
Verified postcode
Seville, Spain
Psychiatric University Hospital (PUK), Zurich
Verified postcode
Zurich, Switzerland

Common questions

What is psychosis?

Psychosis is a mental health condition where someone might experience difficulties telling what's real from what isn't. This can include seeing or hearing things others don't (hallucinations) or having strong beliefs that aren't based in reality (delusions).

What is clozapine?

Clozapine is a medication often prescribed for psychosis, especially when other treatments haven't worked well enough to control symptoms.

What is CBD?

CBD, or cannabidiol, is a natural compound found in the cannabis plant. Unlike THC, another compound in cannabis, CBD does not make you feel 'high' and is being studied for its potential health benefits.

What is a placebo?

A placebo is a 'dummy' pill that looks just like the real study medication but doesn't contain any active drug. It helps compare the effects of the actual treatment against no treatment, so we can be sure any changes are due to the medication.

Will I know if I'm getting CBD or the dummy pill?

No, neither you nor your study doctor will know whether you are receiving CBD or the placebo until the end of the study. This is called 'double-blind' and helps ensure the study results are fair and unbiased.

How to find out more

Jared Robinson

steptrials@phc.ox.ac.uk Official trial record

Always speak to your GP or specialist before deciding to take part in a study.