• Self-administration of over-the-counter bought CBD is increasingly popular and doctors and pharmacists should be aware of its potential adverse effects.
  • The Food Standards Agency (FSA) is advising people who are pregnant, breastfeeding or taking any medication not to consume non-prescription CBD products. Healthy adults are advised by the FSA to think carefully before taking these products, and to keep their daily intake at, or below, 70mg (about 28 drops of 5% CBD) unless otherwise advised by a healthcare professional.
  • Somnolence (drowsiness), decreased appetite, diarrhoea and raised serum aminotransferases (liver enzymes) were side effects significantly associated with the use of an oral purified CBD solution (100mg/ml) (Epidiolex/Epidyolex®, GW Pharmaceuticals) in a meta-analysis of studies involving 550 patients with Lennox-Gastaut or Dravet syndrome.
  • Other effects found to occur very commonly in treated patients in CBD studies for Lennox-Gastaut or Dravet syndrome were vomiting, pyrexia and fatigue.
  • Reports of somnolence were more frequent in patients also receiving the antiepileptic clobazam.
  • Most serum aminotransferase elevations occurred in the first 30 days of treatment but some occurred up to 18 months after treatment initiation in clinical trials. This adverse effect is more likely to occur in a person who is also receiving valproate (an antiepileptic), higher doses of CBD and (to a lesser extent) clobazam.
  • Theoretically, moderate to severe impairment of kidney or liver function may reduce the clearance and/or excretion of CBD which could increase the risk of side effects occurring. The SPC for Epidyolex® advises that cannabidiol is used with caution in patients with moderate or severe hepatic impairment and recommends a lower starting dose in these patients.
  • CBD-containing products are commonly advertised to be free from tetrahydrocannabinol (THC) but have the potential to contain traces of THC, even after the manufacturing process. THC has psychotropic properties and may contribute to potential adverse effects.
  • The purity of individual products may differ, possibly due to undisclosed ingredients or variation in content of CBD (as well as THC), which will have an effect on potential adverse effects or drug interactions. Anyone wishing to use a CBD containing supplement should ensure they obtain their supply from a reputable source.
  • The FSA has requested that all CBD products sold as food supplements will require a valid novel food authorisation application to be submitted by the 31 March 2021 to meet legal standards on safety and content.
  • Information regarding CBD safety is limited to a few human studies and information should be interpreted cautiously. Further studies are needed to evaluate the full safety profile.


Update history

  1. Removed reference to the UKMi Q&A Cannabis based medicinal products potential drug interactions page as it has been retired.
  1. Published