What post-traumatic stress disorder is
Post-traumatic stress disorder (PTSD) is a mental health condition that can develop after exposure to a traumatic event: actual or threatened death, serious injury, or sexual violence. Core symptom clusters defined in the ICD-11 and DSM-5 include re-experiencing (intrusive memories, flashbacks, nightmares), avoidance of trauma-related thoughts and reminders, persistent perceptions of heightened current threat (hypervigilance, exaggerated startle response), and negative alterations in cognition and mood.
A central feature of PTSD is a failure of fear extinction. In a person without PTSD, a previously threatening stimulus that no longer predicts danger gradually stops triggering a fear response, a process critically dependent on the amygdala, prefrontal cortex, and hippocampus. In PTSD, extinction learning is impaired, so fear responses to trauma reminders persist or worsen. Standard UK treatments recommended by NICE include trauma-focused cognitive behavioural therapy, eye movement desensitisation and reprocessing (EMDR), and in some cases, venlafaxine or sertraline.
The endocannabinoid system is directly involved in the neurobiology of fear extinction, which has made it a focus of PTSD research.
Cannabis research on Post-traumatic stress disorder
The evidence base includes several sources relevant to this condition. However, the most clinically relevant pages come from a single grower handbook that discusses the role of the endocannabinoid system in fear memory processing. The remaining matches are passing mentions in magazine articles or non-cannabis academic texts.
The published medical literature covers three main streams of evidence: human brain imaging of the endocannabinoid system in PTSD, animal research on endocannabinoid-mediated fear extinction, and a small number of human clinical studies.
Endocannabinoid system and fear extinction: animal research and human imaging
A substantial animal research literature, spanning more than two decades, demonstrates that CB1 receptors in the amygdala are required for normal fear extinction. Mice genetically engineered to lack CB1 receptors show impaired extinction of conditioned fear. Conversely, pharmacological enhancement of endocannabinoid signalling in the amygdala facilitates fear extinction in rodent models. These are animal findings that identify a candidate mechanism; they do not establish that cannabis is used for PTSD in people.
A human PET imaging study published in 2013 compared CB1 receptor availability in people with PTSD against both healthy controls and trauma-exposed individuals without PTSD. The study found that people with PTSD showed elevated CB1 receptor availability in the amygdala and anterior cingulate cortex, suggesting altered endocannabinoid signalling in the brain regions responsible for fear processing. This is human neuroscience evidence, not treatment evidence. It shows the system is different in PTSD but does not tell us whether adding exogenous cannabinoids helps, harms, or does nothing.
Another human study found reduced circulating concentrations of the endocannabinoid anandamide in people with PTSD compared with controls, providing further evidence of altered endocannabinoid tone.
Human clinical studies: nabilone
Nabilone, a synthetic cannabinoid that acts as a THC analogue, has been studied in one randomised controlled trial for PTSD. The 2015 Canadian trial enrolled 10 male military personnel with PTSD and treatment-resistant nightmares and compared nabilone against placebo in a double-blind crossover design. Nabilone was associated with a statistically significant reduction in nightmare frequency and severity, and improved sleep, measured by the Clinician-Administered PTSD Scale (CAPS) nightmare item and the Pittsburgh Sleep Quality Index. This was a human clinical study. It was also small: 10 participants, all male, all military, and it tested a single synthetic THC analogue, not cannabis. The trial examined nightmares, not PTSD as a whole.
A small open-label human study from 2014 tested THC (5 mg twice daily) in 10 people with chronic PTSD. After three weeks, participants showed reduced CAPS scores. This was an open-label study without a placebo control group, so placebo effect and expectation cannot be ruled out.
Human observational studies
Several observational studies from Canada and the United States have surveyed military veterans and other people with PTSD who use cannabis. These surveys consistently report that some people with PTSD describe cannabis as helpful for sleep, nightmares, and anxiety. Observational data from self-selected respondents cannot distinguish pharmacological effect from placebo response, natural recovery, concurrent treatment changes, or the effects of expectation and social context. These studies identify that people with PTSD are using cannabis, not that cannabis is an effective or safe PTSD treatment.
Larger-scale evidence reviews
A 2019 systematic review and meta-analysis of cannabinoids for mental disorders, published in the Lancet Psychiatry, examined the available evidence for PTSD and concluded there was insufficient evidence to support cannabinoid treatment. The review identified that the existing trials were too small and too few to draw clinical conclusions.
A 2017 systematic review of cannabis and PTSD came to the same conclusion: the available evidence is inadequate to determine whether cannabis is effective or safe for PTSD.
Compounds studied for Post-traumatic stress disorder
THC is the cannabinoid most directly implicated in fear extinction biology. CB1 receptor activation in the amygdala is necessary for extinction learning in animal research. The single human RCT of a cannabinoid for PTSD tested nabilone, a synthetic THC analogue. THC has also been studied in human PET imaging research showing altered CB1 receptor availability in PTSD.
CBD has been studied in animal models of fear extinction and has been shown to facilitate extinction learning when administered before extinction training in rats. CBD’s anxiolytic effects, demonstrated in human experimental studies (see the anxiety disorders page), are also relevant to PTSD, but no human RCT of CBD for PTSD has been published. CBD is being investigated in an ongoing clinical trial for PTSD (NCT04197102), but results are not yet available.
CBG has not been tested in any human PTSD study. Animal research on CBG for anxiety-like behaviour exists, but PTSD-specific animal models using CBG are absent.
Beta-caryophyllene is a CB2 receptor agonist. Animal research has demonstrated that CB2 receptor activation can modulate stress and anxiety-related behaviour. The relevance of CB2-mediated effects to the core pathology of PTSD (fear extinction, amygdala function) is less direct than CB1-mediated mechanisms. No human PTSD trial of beta-caryophyllene exists.
Linalool has been studied in rodent models for sedative and anxiolytic-like effects. No human PTSD data is available.
Limonene has shown anxiolytic-like effects in preclinical research, but these findings are from generalised anxiety models and there are no human PTSD studies.
Limits of the evidence for Post-traumatic stress disorder
The gap between the neuroscience and the clinical evidence for PTSD is one of the largest for any condition in this series. The endocannabinoid system is demonstrably involved in fear extinction at the receptor, cellular, and brain-circuit level. Animal research spanning decades and human PET imaging studies both support this biological connection. But the only human randomised controlled trial of a cannabis-related medicine for PTSD enrolled 10 people and tested a synthetic analogue, not cannabis. The trial measured nightmares, not the full PTSD syndrome.
No randomised controlled trial of whole-plant cannabis for PTSD has been published. No trial has tested whether cannabis, in any form, improves the core symptoms of re-experiencing, avoidance, or hyperarousal in people with PTSD.
The observational data tells us that people with PTSD are using cannabis and that some report subjective benefit. This does not fill the gap left by the absence of controlled trials. Many people with PTSD also drink alcohol to manage symptoms, and alcohol is harmful for PTSD outcomes in the long term. Patient report alone does not confirm safety or effectiveness.
The biological plausibility is strong, stronger for PTSD than for most other conditions. But a mechanism is not a treatment, and no clinical trial has established that adding external cannabinoids to a system that is already altered in PTSD produces a net benefit.
NICE guideline NG116 (2018) for PTSD does not mention cannabis-based medicinal products. NICE’s separate cannabis guideline (NG144) considered chronic pain, intractable nausea, and severe treatment-resistant epilepsy; it did not review PTSD.
Sources
1. Jetly R, Heber A, Fraser G, Boisvert D. The efficacy of nabilone, a synthetic cannabinoid, in the treatment of PTSD-associated nightmares: a preliminary randomized, double-blind, placebo-controlled cross-over design study. Psychoneuroendocrinology. 2015;51:585-588. Study record
2. Neumeister A, Normandin MD, Pietrzak RH, et al. Elevated brain cannabinoid CB1 receptor availability in post-traumatic stress disorder: a positron emission tomography study. Molecular Psychiatry. 2013;18(9):1034-1040. Study record
3. Black N, Stockings E, Campbell G, et al. Cannabinoids for the treatment of mental disorders and symptoms of mental disorders: a systematic review and meta-analysis. Lancet Psychiatry. 2019;6(12):995-1010. Study record
4. Hill MN, Bierer LM, Makotkine I, et al. Reductions in circulating endocannabinoid levels in individuals with post-traumatic stress disorder following exposure to the World Trade Center attacks. Psychoneuroendocrinology. 2013;38(12):2952-2961. Study record
5. O’Neil ME, Nugent SM, Morasco BJ, et al. Benefits and harms of plant-based cannabis for posttraumatic stress disorder: a systematic review. Annals of Internal Medicine. 2017;167(5):332-340. Study record
6. Marsicano G, Wotjak CT, Azad SC, et al. The endogenous cannabinoid system controls extinction of aversive memories. Nature. 2002;418(6897):530-534. Study record
