Not yet recruitingNAINTERVENTIONAL

Exploring The Effect Of Cannabidiol On Cannabis Tolerance Using A Novel Vaporiser Device In Heavy Users (Stage 1)

This study aims to understand cannabis tolerance, which is when heavy users need more THC (the main intoxicating compound in cannabis) to feel the same effects. We're investigating if CBD, another cannabis compound that doesn't cause a high, can change how much THC heavy users consume to get their usual feeling. We're also developing a new, safe way for participants to use THC with a vaporiser in a controlled setting. About 30 adults who use cannabis heavily will take part. The results will help us learn more about tolerance and how CBD might influence THC's effects.

At a glance

Status

Not yet recruiting

Phase

Sponsor

King's College London

Enrolment target

Start

01 Mar 2026

Estimated completion

01 Dec 2026

Cannabis Intoxication

What is this study about?

You might know that cannabis contains different compounds. One important one is called delta-9-tetrahydrocannabinol, or THC for short. This is the part that makes people feel 'high' or intoxicated. If someone uses cannabis often and heavily, their body can get used to THC. This means they might need to use more and more of it to get the same effects, a process called developing 'tolerance'.

Another compound found in cannabis is called cannabidiol, or CBD. Unlike THC, CBD doesn't make you feel high. Some people believe CBD might affect how THC works in the body and brain, but we don't fully understand if it can change how heavy cannabis users respond to THC. This study wants to find out if taking CBD can influence how much THC heavy users need to feel their usual level of intoxication.

To do this, we're first developing a new, safe method for people to use THC in a lab setting, using a vaporiser similar to what some people use at home. This will allow us to carefully measure how much THC is used. The study will involve about 30 adults who are heavy cannabis users. We'll be looking at how THC consumption changes, along with mood, thinking skills, and some physical measures like heart rate. This research will help us learn more about how tolerance develops and if CBD could play a role in how people experience the effects of THC.

Key takeaways

Looks at how CBD might change THC effects in heavy cannabis users.
Developing a new, safe way to study THC use in a lab.
Open to heavy cannabis users aged 18-45.
Involves two main sessions where participants receive CBD or a placebo.
Aims to improve understanding of cannabis tolerance and CBD's role.
Participation helps future cannabinoid research.

Who may be eligible?

To join this study, you need to be an adult between 18 and 45 years old. You should be a heavy cannabis user, meaning you typically use between 7 and 14 grams of strong cannabis per week, on at least 5 days a week, for the past month. You also need to be able to pass a urine drug test for cannabis (but be negative for other illegal drugs) and a breath test for alcohol. You'll need to agree to not use cannabis for 4 hours before any study sessions and be willing to eat two fatty yoghurts to help with medicine absorption.

There are certain reasons why you might not be able to take part. For example, if you have a history of serious mental health conditions like psychosis or bipolar disorder (either yourself or a close family member), or if you're currently taking certain medications (like antidepressants, mood stabilisers, or some heart or seizure medications). Also, if you regularly use alcohol or other illegal drugs (besides cannabis or tobacco/nicotine) or have a major medical condition that the study doctor thinks makes it unsafe for you to join. Pregnant or breastfeeding women, or those unwilling to use contraception, cannot participate.

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 18 and 45 years old?
Do you use cannabis heavily (7-14g/week, 5+ days/week)?
Can you provide a urine sample that shows cannabis but no other illegal drugs?
Are you able to abstain from cannabis for 4 hours before study sessions?
Do you have a personal or close family history of psychosis or bipolar disorder?
Are you currently taking regular medication for a serious medical condition?

Answer every question to see your result.

What does participation involve?

If you join this study, it will be done in two main parts. In the first part, called pilot sessions, you'll help us test and fine-tune a new method for safely using THC with a vaporiser in the lab. This is to make sure the procedure is reliable for everyone.

In the second part, you'll come to two separate study sessions. In each session, you'll receive either a single dose of CBD or a 'dummy' pill (placebo) by mouth. You won't know which one you're getting, and neither will the study team. After taking the pill, you'll use a vaporiser to inhale THC and decide when you've had enough based on how you feel. The order of the CBD and placebo sessions will be random, and there will be a break between them.

Throughout these sessions, we'll measure how much THC you use, assess your mood, thinking abilities, and general mental well-being. We'll also check your heart rate and blood pressure, and take blood samples to measure levels of THC and CBD in your system. We anticipate your total involvement will span several weeks.

Potential risks and benefits

Participating in this study might offer some potential benefits, such as gaining a better understanding of how cannabis affects you personally. Your involvement also contributes valuable knowledge that could help us understand cannabis tolerance and the role of CBD for many people. Every study has potential risks, and in this one, you will be using THC, which can cause intoxication and temporary changes in mood, thinking, and physical measures like heart rate. We will monitor you closely during sessions. You are free to withdraw from the study at any time, for any reason, without it affecting your usual medical care.

Locations (1)

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

King's Clinical Research Facility
Verified postcode
London, United Kingdom

Common questions

What is 'cannabis tolerance'?

It's when your body gets used to cannabis, so you need to use more of it to get the same effects you used to feel.

What is the difference between THC and CBD?

THC is the part of cannabis that makes you feel 'high'. CBD is another part of cannabis that doesn't make you feel high and is being studied for its other effects.

Will I know if I'm getting CBD or a placebo?

No, this is a 'blinded' study, meaning neither you nor the research team will know if you're getting CBD or the dummy pill until after the study is over.

Is the THC use safe in the study?

Yes, we are carefully developing a new method to administer THC safely in a controlled lab setting, under close supervision.

How long will each study session last?

The information doesn't specify exact session lengths, but they will involve taking a pill, a waiting period, THC administration, and various measurements.

How to find out more

Edward Chesney, MRCPsych PhD

kingscrf@kcl.ac.uk +4420 7836 5454 Official trial record

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