CBD Research

CBD Research

Research and Safety: Is CBD Safe?

Research scientist

The scientific research on cannabinoids, including CBD, has increased since the legalisation of cannabis in the USA and Canada, and the approval of medicinal cannabis as a medication for specific conditions in the UK. Prior to this, it was difficult to obtain the licenses and approval required to study Cannabis Sativa. 

CBD Research Study Findings

Various CBD formulations have been tested in pre-clinical studies and found to have diverse medicinal properties, such as anti-nausea, anti-emetic (prevents vomiting), anti-tumour, anti-inflammatory, antidepressant, anti-psychotic, and anti-anxiolytic (prevents anxiety). 1. Recent research studies have examined the effectiveness of CBD in treating a number of ailments including seizure disorders, anxiety disorders, psychosis/ schizophrenia, pain/spasticity, and Parkinson disease, gastrointestinal disorders 1., 2., 3. and substance abuse disorders. 2., 4. There is strong evidence supporting the utility of CBD to treat epilepsy. For other health conditions reviewed, evidence was often mixed and/or there was a general lack of well-powered randomized, placebo-controlled studies to draw definitive conclusions, so further research is required. 3., 5.

One of the difficulties in directly comparing the results of different research studies to determine the effectiveness of CBD, is that the experimental protocols were significantly different, as was the dose of CBD administered. However, one review of randomised controlled trials administering CBD (by oral solution, capsules, or oromucosal spray), found that an average dose of 14 mg/Kg/day was reported in positive outcome trials, compared to 5 mg/Kg/day average dose reported in trials in which CBD did not demonstrate efficacy. 6. These high oral doses that are required for efficacy are likely to increase the side effects of CBD.

Research Findings: Common Side-effects

The most common, reported side effects of CBD include “somnolence (sleepiness); decreased appetite; diarrhoea; transaminase (liver enzyme) elevations; fatigue, malaise (lack of energy), and asthenia (loss of strength); rash; insomnia, sleep disorder, and poor-quality sleep; and infections”, in addition to causing mild to severe hepatic (liver) impairment in some trials. 1. Recent studies using CBD showed that most acute and prolonged adverse effects of CBD are mild to moderate, with serious adverse effects being rare and usually occurring through drug interactions. 2.,7. most studies reported no adverse effects with acute administration and mild to moderate adverse effects with chronic administration.

In comparison, the side effect profile of CBD products is better than other drugs. 2. CBD works with the body’s endocannabinoid system, which varies slightly from individual to individual. This, along with individual differences in human physiology, means that CBD affects each individual slightly differently and will be more effective for some people and less effective for others. The higher the dose of CBD taken, the higher the chance of unwanted side effects occurring, so it is important that you find the dose most effective to you.

CBD Safety Concerns

The FSA are concerned with the safety of CBD. It recommends that healthy adults do not take more than 70 mg a day in total, unless otherwise advised by a doctor. 8. They noted that signs of adverse effects on the liver were seen at a CBD dose of 5 mg/kg body weight in patients and in healthy human volunteers (equivalent to 350 mg in a 70 kg adult). However, adverse effects on the liver might occur at lower doses, more research is required to determine this. CBD has also been shown to cause inhibitory interactions with some medications at doses of 1 mg/kg body weight/day. Therefore, until further data are available, 1 mg/kg body weight/day of CBD is seen as a pragmatic upper limit of intake, above which there would be clear concerns about safety. 8. CBD is not considered to be safe for pregnant or breastfeeding women.

NEXT: “Prescription Medication and CBD


1. Pauli, C.S., Conroy, M., Heuvel, B.D.V. and Park, S.H., 2020. Cannabidiol drugs clinical trial outcomes and adverse effects. Frontiers in Pharmacology11.

2. Larsen, C. and Shahinas, J., 2020. Dosage, efficacy and safety of cannabidiol administration in adults: a systematic review of human trials. Journal of clinical medicine research, 12(3), p.129.

3. White, C.M., 2019. A review of human studies assessing cannabidiol’s (CBD) therapeutic actions and potential. The Journal of Clinical Pharmacology, 59(7), pp.923-934.

4. Capano, A., Weaver, R. and Burkman, E., 2020. Evaluation of the effects of CBD hemp extract on opioid use and quality of life indicators in chronic pain patients: a prospective cohort study. Postgraduate Medicine, 132(1), pp.56-61.

5. Sholler, D.J., Schoene, L. and Spindle, T.R., 2020. Therapeutic Efficacy of Cannabidiol (CBD): a Review of the Evidence From Clinical Trials and Human Laboratory Studies. Current Addiction Reports, pp.1-8.

6. Millar, S.A., Maguire, R.F., Yates, A.S. and O’Sullivan, S.E., 2020. Towards better delivery of cannabidiol (CBD). Pharmaceuticals, 13(9), p.219.

7. Dos Santos, R.G., Guimarães, F.S., Crippa, J.A.S., Hallak, J.E., Rossi, G.N., Rocha, J.M. and Zuardi, A.W., 2020. Serious adverse effects of cannabidiol (CBD): a review of randomized controlled trials. Expert Opinion on Drug Metabolism & Toxicology, 16(6), pp.517-526.

8. Committee on Toxicity, 2020. Position paper on the potential risk of CBD in CBD food products. Available at https://cot.food.gov.uk/sites/default/files/2020-08/cbdpositionpaper290720_accessibleinadobepro.pdf

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