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Drug reviews: use, side effects, effectiveness

Cannabidiol, CBD oil

Cannabidiol (CBD) oil has reached its presence most pharmacies and supermarkets in UK. It is widely available online and due to its coverage in media it is growing in popularity.

CBD oil (also sold under name of hemp oil) is produced by extraction of cannabidiol from the hemp plant. Cannabidiol is one of over 100 cannabinoids which are present in cannabis plant.

Hemp plants are normally used in production of CBD oils as these are high in cannabidiol and do not contain tetrahydrocannabinol (THC) in large amounts. THC is the psychoactive cannabinoid which makes people ‘high’ when they use cannabis.

What is CBD oil used for?

Most manufactures of CBD oil claim the following:

  • reduce anxiety and stress and
  • pain relief
  • reduction in inflammation

THC and cannabidiol are currently widely research for medical purposes and has shown to help possibly with anxiety. Small study involving 72 patients who took CBD resulted reduction in patient’s anxiety and improved in sleep. Small number of patients however reported worsening of both symptoms throughout the duration of trial (Shannon et al, 2019). Overall results proven ‘a more sustained response to anxiety than for sleep over time’ (ibid). This study however had its limitations for example lack of randomisation and a very small sample of patients. Antidepressant and anxiolytic properties of CBD oil is possibly due to its partial agonist properties for serotonin 5-HT1A receptor (Russo et al, 2005).

No human studies involving CBD preparations exist to support its claimed anti-inflammatory properties, however an animal study has shown significant reduction in joint swelling in response to transdermal treatment with gel containing CBD (Hammell et al, 2015).

The strongest evidence for cannabidiol effectiveness is in reduction of seizures in Lennox-Gastaut syndrome (LGS), supported with randomized, double-blind, placebo controlled trial (French et al, 2017).

Why CBD oil is placed under the tongue?

Placing CBD oil under the tongue allows for quicker absorption into your body as compared for example with oral ingestion. Sublingual absorption is very effective, and generally more product will be absorbed and available in your body. Higher bioavailability increases effectiveness of the product. That is why oil drops or spray formulation are preferable for CBD oil.

Is CBD oil legal in UK

CBD oil is legal in UK, however products containing CBD cannot contain more than 0.02% of THC. CBD oil cannot be advertised for medical purposes.

Does CBD oil get you ‘high’?

  1. No. CBD oil sold in UK cannot contain more than 0.02% of THC, the psychoactive cannabidiol which makes people ‘high’.

What are the common side effects of CBD oil?

Some studies identified the following side effects when taking CBD oils (SPS NHS, 2018):

  • somnolence (sleepiness) ,
  • decreased appetite,
  • vomiting,
  • diarrhoea and
  • elevated liver enzymes

Does CBD oil interact with other medications?

Like many other drugs, CBD oil is metabolised by the liver. In vitro studies (in the laboratory) suggest CBD oil is potent inhibitor of different liver enzymes. Liver inhibitors can increase plasma concentration of other drugs metabolised by the same enzyme. Some interactions known to be reported with CBD oils include interactions with anticoagulants (e.g. warfarin) and antiepileptic medicines, however the exact degree of interactions is not know. You should inform your doctor if you are planning to use CBD oil and currently take other medications. For more information visit ‘Cannabis based medicinal products potential drug interactions‘ (ibid).

What other cannabis / cannabidiol preparations are available in UK?

The only licensed preparation containing both THC and CBD in UK is Sativex, which contains mix of THC and CBD. Sativex is only licensed for treatment of spasticity in multiple sclerosis. Due to high cost of this medication NICE does not recommend to prescribe it to patients.

I heard news on Tv about medicinal cannabis, what is it?

Epidiolex is currently going trough a process of licensing approval. Epidiolex is ‘a highly purified liquid containing CBD (NHS, 2018). Epidiolex does not contain THC. Epidiolex has already been approved in USA for for treatment of two epilepsy disorders. In UK is can currenlty be prescribed as unlicensed medicine for treatment of Lennox-Gastaut syndrome and Dravet syndrome (rare forms of epilepsy).


More research is needed to support benefits claims and safety of CBD oil. Large, well designed clinical studies would be preferable; however this is unlikely to happen due to costs involved and due to the fact that CBD oils are already sold as food supplement. Understanding how CBD act in the body would be also beneficial since, the mechanism of action of cannabidiols is not fully determined.


French et al (2017). Cannabidiol (CBD) significantly reduces drop seizure frequency in Lennox-Gastaut syndrome (LGS): results of a multi-center, randomized, double-blind, placebo controlled trial. Available at: Accessed on 06/03/2019

Hammell et al (2015). Transdermal cannabidiol reduces inflammation and pain-related behaviours in a rat model of arthritis. Accessed on 06/03/2019

NHS (2018). Medical cannabis (and cannabis oils). Available at: Accessed on 06/03/2019

Russo et al (2005). Agonistic Properties of Cannabidiol at 5-HT1a Receptors. Available at: Accessed on 06/03/2019

Shannon et al (2019). Cannabidiol in Anxiety and Sleep: A Large Case Series. Accessed on 06/03/2019

SPS NHS, Specialist Pharmacy Service (2018). Cannabidiol oil – potential adverse effects and drug interactions. Available at: Accessed on 06/03/2019

Szkudlarek et al (2018). Δ-9-Tetrahydrocannabinol and Cannabidiol produce dissociable effects on prefrontal cortical executive function and regulation of affective behaviors. Available at: Accessed on 06/03/2019

I am a community pharmacist working in UK. I blog about drugs, health and pharmacy.

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