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CBD research: what the evidence shows

(Cannabidiol) The non-intoxicating cannabinoid studied for epilepsy, anxiety, and inflammation, with a pharmacology distinct from THC.

State of the evidence

Synthesized

Synthesized from 25 studies in the library · AI-generated, grounded in the abstracts below

Found by searching the library for CBD, cannabidiol, epidiolex, then ranked by relevance.

The research on CBD is broad but uneven. In controlled human studies, CBD is generally safe and well tolerated, and it can blunt some THC effects (paranoia, memory impairment, arousal to fearful faces), though several small trials found no effect of CBD alone versus placebo, and one found CBD did not reduce THC-induced driving impairment. Evidence for therapeutic benefit (anxiety, psychosis) is promising but mostly indirect, from small samples, single doses, or reviews, with dose-response effects (e.g., only 300 mg reduced anxiety) and limited long-term or clinical-outcome data.

Evidence by study

Direction is which way each study's own result points, not our rating of the study.

What the directions mean
Supports:
the study found the intervention worked, or its hypothesis held.
Opposes:
it found the opposite, no benefit or a harm.
No effect:
no significant difference either way.
Mixed:
effects in both directions within the same study.
Unclear:
the abstract does not report a direction.
Study Design Sample size Direction Finding
Cannabidiol inhibits THC-elicited paranoid symptoms and hippocampal-dependent memory impairment 2012 RCT 48 Supports Pre-treatment with 600 mg oral CBD reduced THC-elicited paranoia and clinically significant positive psychotic symptoms and mitigated THC-induced episodic memory impairment.
Distinct Effects of Δ9-Tetrahydrocannabinol and Cannabidiol on Neural Activation During Emotional Processing 2009 double-blind randomized placebo-controlled crossover 15 Supports CBD showed a trend toward reduced anxiety and decreased skin conductance fluctuations and limbic activation during fearful face processing, whereas THC increased anxiety and arousal.
Cannabidiol, a Cannabis sativa constituent, as an antipsychotic drug 2006 review Supports Reviews animal and human evidence suggesting CBD has anxiolytic-like and antipsychotic-like properties and may be a safe, well-tolerated alternative treatment for schizophrenia.
Translational Investigation of the Therapeutic Potential of Cannabidiol (CBD): Toward a New Age 2018 review Supports Reports that CBD shows anxiolytic, antipsychotic, and neuroprotective properties and has been investigated across epilepsy, substance use, schizophrenia, anxiety disorders, depression, sleep, and Parkinson's disease, while noting controlled trials are still needed.
Inverted U-Shaped Dose-Response Curve of the Anxiolytic Effect of Cannabidiol during Public Speaking in Real Life 2017 RCT 60 Mixed Only 300 mg CBD reduced anxiety scores versus placebo in the post-speech phase, while 100 mg and 900 mg did not, indicating an inverted U-shaped dose-response.
Acute Effects of a Single, Oral dose of d9-tetrahydrocannabinol (THC) and Cannabidiol (CBD) Administration in Healthy Volunteers 2012 randomized double-blind crossover placebo-controlled trial 16 No effect CBD 600 mg produced no differences from placebo on any symptomatic or physiological measure, while THC produced anxiety, dysphoria, psychotic symptoms, sedation, and increased heart rate.
Modulation of Mediotemporal and Ventrostriatal Function in Humans by Δ9-Tetrahydrocannabinol 2009 randomized double-blind placebo-controlled within-subject trial 15 No effect THC increased psychotic symptoms, anxiety, intoxication, and sedation and altered brain activation during verbal learning, whereas CBD had no significant effects on these measures.
The neuropsychopharmacology of cannabis: A review of human imaging studies 2018 review Mixed Reviews human neuroimaging evidence that cannabis and THC acutely affect executive, emotional, reward, and memory systems, and notes that CBD may offset some of these acute effects.
Neuroimaging in cannabis use: a systematic review of the literature 2009 systematic review Unclear Reviews neuroimaging studies of cannabis and reports inconsistent activation findings and minimal evidence of structural brain changes, with CBD mentioned only as a search term.
Cannabidiol (CBD) content in vaporized cannabis does not prevent tetrahydrocannabinol (THC)-induced impairment of driving and cognition 2019 randomized double-blind within-subjects crossover 14 Opposes Cannabis with equivalent CBD and THC was no less impairing than THC-dominant cannabis on simulated driving and cognition, and impairment on some cognitive tasks was worse with the CBD/THC product.
Acute and chronic effects of cannabinoids on effort-related decision-making and reward learning: an evaluation of the cannabis ‘amotivational’ hypotheses 2016 randomized controlled trial 17 Mixed THC-only cannabis reduced high-effort choices relative to placebo, while adding CBD to THC did not produce that reduction; cannabis dependence was linked to weaker reward learning but not to differences in effort-based choice.
Plastic and Neuroprotective Mechanisms Involved in the Therapeutic Effects of Cannabidiol in Psychiatric Disorders 2017 review Supports Proposes that CBD's benefits in psychiatric disorders involve neuroplastic changes, including protection against stress-induced reductions in hippocampal neurogenesis and dendrite spine density and prevention of microglial activation and GABA neuron loss in a schizophrenia model.
Tolerance and cross-tolerance to neurocognitive effects of THC and alcohol in heavy cannabis users 2010 double-blind placebo-controlled three-way study 21 No effect Heavy cannabis users showed tolerance to THC's impairing effects on neurocognitive tasks and no cross-tolerance to alcohol; THC generally did not affect task performance, though combined THC and alcohol worsened divided attention.
Modulation of effective connectivity during emotional processing by Δ9-tetrahydrocannabinol and cannabidiol 2009 randomized double-blind placebo-controlled fMRI trial 15 Supports CBD, but not THC, disrupted forward connectivity between the amygdala and anterior cingulate during processing of fearful faces, proposed as a correlate of its anxiolytic properties.
Neurophysiological and subjective profile of marijuana with varying concentrations of cannabinoids 2005 randomized controlled trial 23 No effect Varying CBD (and cannabichromene) concentrations in smoked marijuana did not change subjective, behavioral, or neurophysiological responses, whereas THC produced the expected effects.
Effects of delta-9 tetrahydrocannabinol and cannabidiol on cognitive outcomes following acute use of cannabis for chronic pain. 2026 observational study 183 Mixed CBD-dominant users outperformed CBD+THC users in working memory one hour post-use and had more stable verbal learning than THC or CBD+THC users, with no significant effects on executive function, episodic memory, or processing speed.
Physical Activity Level Moderates Cannabis-Associated Reductions in Negative Affect in Anxious Individuals. 2026 secondary analysis of an RCT 178 Mixed Negative affect decreased over time in all cannabis groups, but physical activity moderated this decrease only in the THC-dominant group, not in the CBD-dominant or THC+CBD groups.
The Potential of Cannabidiol for the Treatment of Psychosis: Endocannabinoid Regulation of Serotonergic Neurotransmission via Serotonin 5-HT1A/2A Receptors. 2026 review Supports Argues that CBD's receptor-level actions (negative allosteric CB1 modulation, antagonism of THC, engagement of GPR55, TRPV1, ENT1) explain its therapeutic profile and low addiction liability and provide a rationale for exploring CBD in psychosis.
Metabolic and respiratory alterations following acute exposure to high-THC and high-CBD cannabis smoke in female mice 2026 controlled laboratory experiment in mice Mixed Body temperature dropped after placebo, high-CBD, and high-THC smoke, with placebo and high-CBD smoke appearing additive to the high-THC effect, while increases in ventilation and tidal volume were mainly attributable to THC.
Does co-administration of cannabidiol (CBD) influence the plasma availability of delta-9-tetrahydrocannabinol (THC) and its active metabolite in humans? A systematic review and meta-analysis. 2026 systematic review and meta-analysis 341 Supports CBD co-administration significantly increased average THC AUCt and increased Cmax and AUCt of the active metabolite 11-OH-THC, with very low to medium certainty evidence.
CB1 receptor-enriched functional connectivity analysis revealed target-specific modulation by cannabidiol in early psychosis. 2026 randomized double-blind placebo-controlled crossover 27 Supports A single 600 mg dose of CBD reduced CB1 receptor-enriched functional connectivity of the right insular cortex relative to placebo in early psychosis, after which patients no longer differed from healthy controls.
Cannabis and Mental Health: A Systematic Review and Meta-analysis of the Neuropsychiatric Effects, Therapeutic Potentials, and Policy Implications of THC and CBD 2026 systematic review and meta-analysis 14 Mixed THC was consistently associated with increased psychotic symptoms, cognitive impairment, and anxiety, whereas CBD showed potential antipsychotic, anxiolytic, and neuroprotective effects; evidence for cannabis products in psychiatric disorders was limited to modest short-term benefits.
Synthetic Pathway of Nonpsychoactive Cannabidiol from Psychoactive Tetrahydrocannabinol: A DFT Guide. 2026 theoretical or computational chemistry study Unclear Proposes a two-step reaction pathway converting THC to CBD via boron trichloride and a selective base, with a rate-determining transition state and a highly exergonic overall reaction.
Acute behavioural effects of low-dose cannabidiol: A randomised crossover trial in healthy volunteers. 2026 randomized controlled crossover trial 70 Supports A 200 mg dose of synthetic CBD produced a 12.8% higher peak pleasant drug effect score than placebo, while 20, 50, and 100 mg showed no significant effect; adverse events were mild or moderate.
Prenatal Cannabidiol and Δ9-Tetrahydrocannabinol exposure lead to sex-specific disruptions in risk assessment and behavioral switching via divergent rewiring of the adult mPFC 2026 observational animal study Opposes Prenatal CBD and THC both increased repetitive behavior and abolished endocannabinoid long-term depression in prefrontal cortex neurons, with sex-specific circuit changes in CBD-exposed offspring.

Points of agreement

  • CBD is generally safe and well tolerated in human studies, with no marked acute intoxication or physiological effects at tested doses.
  • CBD can attenuate some THC effects, including paranoia, psychotic symptoms, memory impairment, and arousal to fearful faces.
  • Reviews and mechanistic work consistently describe anxiolytic, antipsychotic, and neuroprotective potential for CBD.
  • CBD's effects appear dose-dependent, with non-linear or inverted U-shaped dose-response patterns.

Conflicts

  • Some controlled trials find CBD reduces THC-induced paranoia and memory impairment, while others find no effect of CBD alone versus placebo on symptoms or physiology.
  • One study found CBD did not reduce THC-induced driving and cognitive impairment and may worsen some cognitive measures, contrary to the mitigating-effects hypothesis.
  • CBD co-administration increased THC and metabolite plasma exposure in meta-analysis, which complicates claims that CBD simply offsets THC effects.
  • Anxiolytic effects were seen at 300 mg but not at 100 or 900 mg, and a separate trial found a mild pleasant drug effect only at 200 mg, indicating inconsistent dose-response findings.

Gaps

  • Most human trials are small (roughly 14-70 participants) and use single acute doses, so durability and repeated-dose effects are largely unstudied.
  • Long-term clinical efficacy for psychiatric conditions is not established; reviews call for larger controlled trials.
  • Dose-response is poorly characterized, with non-linear effects and few direct dose comparisons.
  • Blinding integrity and expectancy effects are rarely assessed, particularly for subjective outcomes.
  • Populations are narrow (mostly healthy young male volunteers or small patient samples), limiting generalizability.
  • Interactions with THC pharmacokinetics and the clinical implications of increased THC exposure with CBD are unresolved.
Browse these studies in the library

Common questions

What does the research agree on about CBD?
  • CBD is generally safe and well tolerated in human studies, with no marked acute intoxication or physiological effects at tested doses.
  • CBD can attenuate some THC effects, including paranoia, psychotic symptoms, memory impairment, and arousal to fearful faces.
  • Reviews and mechanistic work consistently describe anxiolytic, antipsychotic, and neuroprotective potential for CBD.
  • CBD's effects appear dose-dependent, with non-linear or inverted U-shaped dose-response patterns.
Where do studies on CBD conflict?
  • Some controlled trials find CBD reduces THC-induced paranoia and memory impairment, while others find no effect of CBD alone versus placebo on symptoms or physiology.
  • One study found CBD did not reduce THC-induced driving and cognitive impairment and may worsen some cognitive measures, contrary to the mitigating-effects hypothesis.
  • CBD co-administration increased THC and metabolite plasma exposure in meta-analysis, which complicates claims that CBD simply offsets THC effects.
  • Anxiolytic effects were seen at 300 mg but not at 100 or 900 mg, and a separate trial found a mild pleasant drug effect only at 200 mg, indicating inconsistent dose-response findings.
What is still unknown about CBD?
  • Most human trials are small (roughly 14-70 participants) and use single acute doses, so durability and repeated-dose effects are largely unstudied.
  • Long-term clinical efficacy for psychiatric conditions is not established; reviews call for larger controlled trials.
  • Dose-response is poorly characterized, with non-linear effects and few direct dose comparisons.
  • Blinding integrity and expectancy effects are rarely assessed, particularly for subjective outcomes.
  • Populations are narrow (mostly healthy young male volunteers or small patient samples), limiting generalizability.
  • Interactions with THC pharmacokinetics and the clinical implications of increased THC exposure with CBD are unresolved.
How we analyze this

This synthesis reads the 15 most-cited and 10 most recent studies whose primary subject is CBD, up to 25 in all. The most-cited set anchors the established evidence, and the recent set surfaces work that is too new to have gathered citations yet.

A study qualifies only when CBD or a known alias appears in its title or keywords, so broad reviews that mention it only in passing are left out. Each study is read from its abstract, strongest evidence first, and the summary reports the direction of the results along with any conflicts and gaps.

The full method, including what a person does and does not review, is on the methods page.

Ask your own question in the Research Synthesis Tool

375 articles · 78 from the last two years · 133,396 participants across 149 studies reporting sample size

Common study designs

review 79 systematic review 25 experimental study 11 observational cohort 16 randomized controlled trial 36

Research volume by year

Compare topics →

219 studies whose primary subject is CBD since 2005

Studies about CBD per year, 2005 to 2026, peaking at 30 in 2023 Bar chart: one bar per year, taller where more studies were published that year. 0 15 30 2005 2010 2015 2020 2025
2026 is partial
Show the numbers
Studies about CBD per year, 2005 to 2026, peaking at 30 in 2023
Year Studies
2005 1
2006 2
2007 0
2008 3
2009 7
2010 7
2011 6
2012 3
2013 2
2014 4
2015 3
2016 5
2017 12
2018 16
2019 10
2020 9
2021 16
2022 21
2023 30
2024 23
2025 16
2026 23

Research

Synthesize the evidence → Search all →

Developmental exposure to cannabidiol vapor has persistent impacts on adult exploratory behavior and learning

Medical Cannabis and Cannabinoids October 13, 2026 Taylor M. McGillis, Hannah P Stevenson, Willow Leland et al.

Cannabidiol (CBD) is a non-intoxicating phytocannabinoid with purported benefits across a range of pediatric conditions. However, the relative nascency of its integration in human populations has precluded a longitudinal safety assessment when used during different developmental periods. We hypothesized that CBD’s pharmacodynamic actions underlying the purported therapeutic effects could impact...

DOI: 10.1159/mca/adoag005 (opens in new tab)

Effects of delta-9 tetrahydrocannabinol and cannabidiol on cognitive outcomes following acute use of cannabis for chronic pain.

Psychopharmacology September 1, 2026 Renée Martin-Willett, Samantha N. Melendez, Kent E. Hutchison et al.

RATIONALE An estimated two-thirds of medical cannabis users in the United States are motivated by chronic pain, but clinical guidance remains guarded as to whether the potential benefit of cannabinoids for pain outweighs potential risks, such as effects on cognition. OBJECTIVES In a study where participants experienced benefits of cannabinoids for pain and tension, we evaluated cannabis effects...

DOI: 10.1007/s00213-026-07157-x (opens in new tab) Full text (opens in new tab)

The Potential of Cannabidiol for the Treatment of Psychosis: Endocannabinoid Regulation of Serotonergic Neurotransmission via Serotonin 5-HT1A/2A Receptors.

Neurochemical Research August 27, 2026 Kazutoshi Yonemura, Nobue Kitanaka, Kazuo Tomita et al.

Cannabis, widely used for both medical and non-medical purposes, primarily contains Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD). Δ9-THC is the main driver of cannabis abuse and of psychological and physical dependence, whereas CBD has limited abuse potential and is even being investigated as a treatment for cannabis use disorder and other conditions. This review aims to clarify how...

DOI: 10.1007/s11064-026-04860-1 (opens in new tab) Full text (opens in new tab) Cannabidiol Cannabis Gpr55 Pharmacotherapy +2

Metabolic and respiratory alterations following acute exposure to high-THC and high-CBD cannabis smoke in female mice

Journal of Cannabis Research August 26, 2026 Ario Safaeian, Kaylen M. Young, John G. Howland et al.

Abstract Background Cannabis use has increased in recent years due to legalization. Smoking cannabis leads to inhalation of ∆9-tetrahydrocannabinol (THC) and cannabidiol (CBD), in addition to other particles and gas in the smoke matrix as a result of combustion. The effect of THC on breathing pattern and metabolism has been characterized, but the influence of CBD and the smoke matrix on...

DOI: 10.1186/s42238-026-00490-0 (opens in new tab)

Does co-administration of cannabidiol (CBD) influence the plasma availability of delta-9-tetrahydrocannabinol (THC) and its active metabolite in humans? A systematic review and meta-analysis.

Neuroscience & Biobehavioral Reviews August 20, 2026 Lucy Chester, Heidar Sharafi, Amani Mahroug et al.

Research on the pharmacokinetic influence of cannabidiol (CBD) on delta-9-tetrahydrocannabinol (THC) has produced equivocal results. We conducted a systematic search following PRISMA guidelines (last search: 24th November 2025, PROSPERO: CRD42023480695). Included studies were acute dosing trials that administered a) a single, fixed dose of THC and b) a matched dose of THC co-administered with...

DOI: 10.1016/j.neubiorev.2026.106910 (opens in new tab) Full text (opens in new tab) Cannabidiol Tetrahydrocannabinol Meta-analysis Pharmacokinetics +1

THC and CBD differentially modulated gut microbiota in the Poly I:C rat model of schizophrenia

Frontiers in Pharmacology August 10, 2026 N. Miguel-Ramiro, N. Lamanna-Rama, M. Casquero-Veiga et al.

Background Disruptions in the gut-brain-microbiota axis are increasingly linked to psychiatric disorders. While cannabinoids possess immunomodulatory and neuroprotective properties, their impact on the microbial architecture during critical neurodevelopmental periods remains poorly understood. This exploratory study investigated whether adolescent treatment with delta-9-tetrahydrocannabinol...

DOI: 10.3389/fphar.2026.1858604 (opens in new tab) Full text (opens in new tab)

CB1 receptor-enriched functional connectivity analysis revealed target-specific modulation by cannabidiol in early psychosis.

Journal of Psychopharmacology August 5, 2026

BACKGROUND: Cannabidiol (CBD) has emerged as a potential antipsychotic treatment, acting as a negative allosteric modulator of cannabinoid type-1 (CB1) receptors within the endocannabinoid system. Although previous neuroimaging studies have shown that CBD induces changes in aberrant brain activity and functional connectivity (FC) in psychosis, they have not directly integrated information about...

DOI: 10.1177/02698811261470456 (opens in new tab)

Cannabis and Mental Health: A Systematic Review and Meta-analysis of the Neuropsychiatric Effects, Therapeutic Potentials, and Policy Implications of THC and CBD

Archives of Psychiatry and Mental Health July 29, 2026 Diamond Onyekachi Okoroezi

Aim: This systematic review and meta-analysis examined the neuropsychiatric effects of cannabis, focusing on the contrasting roles of Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD). It evaluated their associations with psychiatric outcomes, assessed the therapeutic potential of cannabis-based products (CBPs), and identified evidence gaps relevant to clinical practice and mental health...

DOI: 10.29328/journal.apmh.1001067 (opens in new tab)

Synthetic Pathway of Nonpsychoactive Cannabidiol from Psychoactive Tetrahydrocannabinol: A DFT Guide.

The Journal of Organic Chemistry July 24, 2026 Sirilak Kongkaew, Waraporn Parasuk, Vudhichai Parasuk

In this study, a reaction pathway for converting the psychoactive compound Δ9-THC into the nonpsychoactive cannabidiol (CBD) was proposed. Related cannabinoids, including Δ8-THC and cannabinol (CBN), were also examined. The transformation proceeds via two key steps: (i) hydrogen elimination and cyclic ether ring cleavage, and (ii) hydrolysis to form hydroxyl groups, facilitated by boron...

DOI: 10.1021/acs.joc.6c00898 (opens in new tab) Full text (opens in new tab)

Acute behavioural effects of low-dose cannabidiol: A randomised crossover trial in healthy volunteers.

Journal of Psychopharmacology July 15, 2026 Lucy Chester, François-Olivier Hebert, Pamela Lachance-Touchette et al.

BACKGROUND Cannabidiol (CBD) is widely consumed in low-dose products. However, evidence for its psychotropic effects at non-clinical doses is sparse and inconsistent. AIMS To characterise the acute behavioural effects of low-dose synthetic CBD in healthy volunteers. We hypothesised that 200 mg of CBD would produce a greater peak pleasant drug effect than a placebo. METHODS In a triple-blind,...

DOI: 10.1177/02698811261464527 (opens in new tab) Full text (opens in new tab)

Clinical trials

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