delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD)
Vida T400:C20 Blueberry Cookies Medical Cannabis Cartridge (400mg delta-9-tetrahydrocannabinol and 20mg cannabidiol per cartridge)
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Cannabis contains delta-9-tetrahydrocannabinol (THC), which causes intoxication. People who use cannabis frequently often develop tolerance, meaning they need to use more THC to feel the same effects. Cannabidiol (CBD) is another compound found in cannabis that is not intoxicating and may influence how THC affects the body and brain. This study will examine whether taking CBD changes how much THC heavy cannabis users consume to reach their usual level of intoxication. The study will also develop a new laboratory method that allows participants to safely and gradually self-administer THC using a vaporiser, similar to how cannabis is used in real-world settings. The study will include around 30 adults who use cannabis heavily. In the first stage, participants will take part in pilot sessions to help refine the THC administration procedure. In the second stage, participants will attend two study sessions and receive a single oral dose of CBD or placebo, in a random order. After this, they will inhale THC using a vaporiser and decide when to stop based on how intoxicated they feel. Researchers will measure how much THC is used, along with mood, mental health symptoms, thinking abilities, physical measures such as heart rate and blood pressure, and blood levels of THC and CBD. The results will help improve understanding of cannabis tolerance and whether CBD alters responses to THC in heavy cannabis users.
Locally preserved from ClinicalTrials.govOpen ClinicalTrials.govlast source update 2026-03-13
What this record can show
This locally preserved record separates the registered protocol from source-reported registry results. Neither is a treatment recommendation.
Registry facts
Cannabis produces its intoxicating effects mainly through delta-9-tetrahydrocannabinol (THC). People who use cannabis frequently often develop tolerance, meaning they need to consume larger amounts of THC to achieve their usual level of intoxication. Cannabidiol (CBD) is another cannabinoid found in cannabis that does not cause intoxication and may alter how THC affects the body and brain. However, its effects on cannabis tolerance in heavy users are not well understood. This study aims to develop a controlled laboratory method for measuring cannabis tolerance and to investigate whether CBD changes how much THC heavy cannabis users consume. The study is conducted in two stages and will recruit approximately 30 adult heavy cannabis users who do not have a history of psychotic or major medical disorders. In Stage One, participants will take part in pilot sessions to establish a safe and reliable method of THC administration using a handheld vaporiser. Participants will self-administer THC in small doses at regular intervals and decide when they have reached their usual and maximum tolerated levels of intoxication. These pilot sessions will be used to refine the timing, dosing, and outcome measures used in the main experiment. In Stage Two, participants will complete two experimental sessions in a double-blind, randomised, placebo-controlled, crossover design. In each session, participants will receive a single oral dose of CBD (1000 mg) or a matching placebo, followed three hours later by THC administration using the vaporiser. The order of CBD and placebo will be randomised, and sessions will be separated by a washout period. During each experimental session, participants will self-titrate THC intake until they reach their typical desired level of intoxication and may continue until they reach their maximum tolerated level. Cannabis tolerance will be assessed by measuring the amount of THC consumed, based on changes in vaporiser cartridge weight and the number of inhalations required to reach these intoxication levels. Additional outcomes include subjective drug effects, mood, psychotic-like symptoms, cognitive performance, speech measures, physical observations (such as heart rate and blood pressure), and blood levels of THC, CBD, and related biomarkers. Safety will be closely monitored throughout all sessions by trained medical staff. The findings from this study will help establish a novel experimental model of cannabis tolerance and improve understanding of how CBD influences responses to THC in heavy cannabis users.
Linked local records
Local links use governed condition terms or exact source-reported intervention names. They are navigation candidates, not efficacy claims.
Interventions
Vida T400:C20 Blueberry Cookies Medical Cannabis Cartridge (400mg delta-9-tetrahydrocannabinol and 20mg cannabidiol per cartridge)
Eligibility
primary outcomes
Time frame: From initiation of use until the participant reaches their desired level of intoxication (self-titrated), assessed up to 4 hours.
Change in THC cartridge weight
secondary outcomes
Time frame: From initiation of use until the participant reaches their maximum tolerated level of intoxication (self-titrated), assessed up to 4 hours.
Change in THC cartridge weight
Time frame: Baseline; The timepoint at which the participant reaches their desired level of intoxication (self-titrated); The timepoint at which the participant reaches their maximum tolerated level of intoxication (self-titrated), assessed up to 4 hours.
Five-item questionnaire on drug effects
Time frame: Baseline; The timepoint at which the participant reaches their desired level of intoxication (self-titrated); The timepoint at which the participant reaches their maximum tolerated level of intoxication (self-titrated), assessed up to 4 hours.
* Relaxed/Anxious * Sad/Happy * Not paranoid/Paranoid * Thinking clearly/confused * Tired/Energetic
Time frame: Baseline; The timepoint at which the participant reaches their desired level of intoxication (self-titrated); The timepoint at which the participant reaches their maximum tolerated level of intoxication (self-titrated), assessed up to 4 hours.
A Likert scale to rate the participant's level of intoxication
Time frame: Baseline; The timepoint at which the participant reaches their desired level of intoxication (self-titrated); The timepoint at which the participant reaches their maximum tolerated level of intoxication (self-titrated), assessed up to 4 hours.
A 19-item self-report questionnaire designed to assess the severity of cannabis withdrawal symptoms
Time frame: Baseline; The timepoint at which the participant reaches their desired level of intoxication (self-titrated); The timepoint at which the participant reaches their maximum tolerated level of intoxication (self-titrated), assessed up to 4 hours.
A brief assessment tool used to measure craving for cannabis
Time frame: Baseline; The timepoint at which the participant reaches their desired level of intoxication (self-titrated); The timepoint at which the participant reaches their maximum tolerated level of intoxication (self-titrated), assessed up to 4 hours.
An investigator-rated measure of psychotic symptoms.
Time frame: Baseline; The timepoint at which the participant reaches their desired level of intoxication (self-titrated); The timepoint at which the participant reaches their maximum tolerated level of intoxication (self-titrated), assessed up to 4 hours.
A 48-item questionnaire that was developed for use in drug studies to measure psychotic-like experiences
Time frame: Baseline; The timepoint at which the participant reaches their desired level of intoxication (self-titrated); The timepoint at which the participant reaches their maximum tolerated level of intoxication (self-titrated), assessed up to 4 hours.
Time frame: Baseline; The timepoint at which the participant reaches their desired level of intoxication (self-titrated); The timepoint at which the participant reaches their maximum tolerated level of intoxication (self-titrated), assessed up to 4 hours.
Assessment of working memory: Forward Digit Span is the maximum number of digits the participant can correctly repeat in the same order, and Reverse Digit Span is the maximum number of digits the participant can correctly repeat in reverse order.
Publications
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