CBD- The Evidence

What is CBD?

CBD stands for cannabidiol. It is an active ingredient derived from the cannabis or hemp plant. CBD oil does not contain THC, which is the active component of cannabis that causes a ‘high’. CBD oil is legal in the UK provided it contains less than 0.2% THC.

There is good and validated evidence from multiple clinical trials for the use of CBD in the treatment of specific types of epilepsy (note that the epilepsy treatments recently in the news relate to cannabis oil, a different substance containing higher percentages of THC). CBD has grown in popularity in recent months and years due to broad discussions about its multiple other uses and benefits. These off the shelf oils, supplements, extracts and lotions claim to help alleviate anxiety, inflammation, pain and even cancer growth. So is there any evidence behind these claims?

The Evidence?

The simple answer to this question is that there is no simple answer! The fact is that large scale clinical trials to investigate these effects of CBD simply haven’t been done yet. The evidence that we do have comes from mostly phase I trials, which are carried out on cells in a lab, or from animal studies. Although these studies show that CBD may potentially display anxiolytic and anti-inflammatory properties, there is no guarantee that this would correlate with any kind of actual recordable result or benefit for humans in the real world.


Two clinical trials have been carried out to investigate the effects of CBD on anxiety. The first study took 24 patients with untreated Generalised Social Anxiety Disorder, split them into 2 groups and gave half CBD oil and half placebo before asking them to perform a public speaking test. They compared their results to 12 healthy candidates also performing the test. Pre-treatment with CBD significantly reduced anxiety, cognitive impairment and discomfort in the patient’s speech performance. The CBD patients displayed no significant difference from the healthy candidates in cognitive impairment, discomfort and alert factors.  The CBD did not however have any effect on physiological parameters such as heart rate or blood pressure.

This study needs to be interpreted carefully. Firstly, it was carried out on patients with a formal diagnosis of an anxiety disorder. The healthy candidates were not given CBD, therefore no conclusions can be drawn regarding the effects of CBD on those without a formal diagnosis of an anxiety disorder. Secondly, this is an extremely small study with minimal power. (1)

The second study investigating the effects of CBD on anxiety was a retrospective study carried out in an outpatient psychiatric clinic. It looked back at patients with a formal diagnosis by a mental health professional of a sleep or anxiety disorder who had been prescribed CBD. It compared their documentation of anxiety or sleep quality. The study showed anxiety scores decreased within the first month of treatment with CBD, and remained decreased throughout the study, whereas sleep scores improved initially and then fluctuated with no overall improvement.

The main issue with this study is that there is no control group. We have no idea what other treatments the patients were having apart from the CBD, and whether their scores would have improved anyway even if they hadn’t been taking it. This study was once again only conducted on those with a formal psychiatric diagnosis and therefore has no transference to healthy patients. (2)


There are multiple studies showing CBD has an anti-inflammatory effect on cells within a lab environment. One study carried out on rats with single joint knee arthritis showed that transdermal CBD gel significantly reduced joint swelling, spontaneous pain, immune cell infiltration and thickening of the synovial membrane in a dose-dependent manner. (3)


There are also several other conditions in which CBD has been postulated to be beneficial, such as the treatment of Multiple Sclerosis, Depression, Cardiovascular disease and Alzheimer’s disease. In all areas however the research is in similarly early stages, without robust clinical evidence of benefit.


Is CBD Safe?

The World Health Organisation collated a report on CBD in 2017. They concluded that CBD is ‘generally well tolerated with a good safety profile’. Multiple trials in both humans and animals have shown that CBD is not associated with tolerance (needing increasing doses for the same clinical effect) or with dependence and abuse potential. (4)

In 2017, the Medicines and Healthcare products Regulatory Agency (MHRA) announced that if CBD is being advertised for medical purposes, it needs to be licensed. No licenses for CBD oil as a medicine have been granted yet, but the products can still be sold, provided no claims about their medical benefits are made. This means that all CBD being sold is unlicensed, and therefore has no regulation of the dosage, the percentage of CBD present, or the price.

A study in 2017 looked at the labelling accuracy of CBD extracts bought online. It found that the amount of CBD stated on the label was only accurate in 31% of products with a +/- 10% variance allowed. (5)

In the studies discussed above the dosage of CBD ranged widely from 0.6-600mg per day. (6) There is no consensus as to what the correct dose of CBD may be for different conditions.


These factors make it very difficult to be able to recommend taking CBD. It is however an exciting substance to watch for the future, when more robust research has been carried out and there is better evidence for if, when and how to take it.


What are your thoughts? Do you take CBD and what are your experiences? Comment or question below!



  1. https://www.ncbi.nlm.nih.gov/pubmed/21307846
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6326553/
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4851925/
  4. https://www.who.int/medicines/access/controlled-substances/5.2_CBD.pdf
  5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5818782/
  6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4604171/

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