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Does cannabidiol reduce severe behavioural problems in youth with intellectual disability?

Children with Intellectual Disability (ID) can also have Severe Behavioural Problems (SBP). SBP can have a major effect on families. At the moment, dealing with SBP is very difficult. There are drugs that can be used to treat SBP, but these are not always helpful. Also, these drugs can cause side-effects. 

Medical cannabis could possibly be a good treatment for SBP in children with ID. However, there is not enough evidence to know if cannabis works for these children. This study is testing a type of medical cannabis called cannabidiol (CBD). CBD is a legal cannabis extract. CBD does not appear to cause a “high”, which can happen with the other main chemical in cannabis, THC. CBD may be helpful in improving behaviour and may also have fewer side effects than existing medications. The researchers hope to find out if CBD works and if it is safe. 

In this study, we will be comparing CBD treatment to a placebo. A placebo is a medication with no active ingredients or a procedure without any medical benefit. It looks like the real thing but is not. Researchers compare results from participants taking placebo with those taking the study drug to see if the study drug works better or if there is a difference in safety compared with taking nothing. If we determine that your child meets all of the requirements to be in the study, he/she will be randomly assigned (like flipping a coin) to receive either CBD or placebo. Your child will have a 50% (1 in 2) chance of receiving CBD.


You may be eligible to participate in this study if you:

  • Are aged 6-18 years 
  • Have an intellectual Disability (IQ below 70). If the patient has not been assessed in the past 2 years we will conduct cognitive testing to determine eligibility. 
  • Have severe Behavioural Problems. To be assessed by the study team at screening: scores of 18 or higher on the Aberrant Behavior Checklist-Irritability subscale and moderate or higher on the Clinical Global Impressions-Severity scale. 
  • Have had no changes to medication in the 4 weeks prior to randomisation. 

You will not be able to participate in the study if any of the folowing apply to you:

  • Non-English speaking parents
  • Psychosis
  • Are taking clobazam, mTOR inhibitors (e.g sirolimus, tacrolimus), anti-cancer agents, citalopram >20mg/day, escitalopram >10mg/day
  • Abnormal liver function test
  • Abnormal renal function test
  • Currently use medicinal cannabis
  • Are pregnant or intending to become pregnant during the study 
  • Are breastfeeding
  • Have an allergy to cannabidiol or cannabis products.

How to participate

If you are interested in knowing more about this study, please email the study coordinator, Dr Zahra Ayati at

A study team member will then call you to talk about the study and ask you some questions to see if the study is suitable for your child. If so, they will send you some information. After you get this information, you can decide if you want to take part or not.