CBD is arguably one of the biggest health trend of the past two years. Touted as a cure for everything from anxiety and depression to insomnia and pain, with potential relieving benefits for conditions like Alzheimer's, multiple sclerosis and cancer, the market for CBD has swelled to an estimated £300m. Around 1.3 million Britons are said to use the stuff.
An abbreviation of cannabidiol, CBD is a compound found in cannabis plants, often added to foods, oils or lotions. Around four to six million Britons have tried it, often to relieve chronic pain or anxiety, since it was made legal to buy on the high street in 2016. CBD differs from THC, another chemical found in cannabis, in that it doesn't produce the psychoactive effects of THC, which is associated with the high, as well as schizophrenia or psychiatric disorders. Thus, CBD is often espoused as a harmless alternative to more nefarious medication, such as opioids.
However, according to a recent review by the Committee on Toxicity, an independent group of scientists, there could be harmful side effects, from liver damage to diarrhoea. Commenting on the review, which were prepared for the government, the panel's chairman, Professor Alan Boobis of Imperial College London, said: “There are certainly potential side-effects of CBD and those taking it should be aware of these.”
The review looked at data from trials by Cambridge-based GW Pharmaceuticals, the company that produces Epidiolex, an epilepsy medicine containing cannabidiol. According to the trial, there were side effects at all doses tested, ranging from liver damage and lethargy to sedation, tremors, diarrohoea and vomiting.
However, Epidiolex is much stronger than the CBD found on the high street, Professor Boobis acknowledged. And, according to CBD experts, the trial's findings don't necessarily mean CBD users should fret.
“CBD at exceptionally high doses can cause an increase in liver enzymes,” says Professor Mike Barnes, a neurologist and medical cannabis expert. “They return to normal once the medicine is stopped. CBD is extremely safe. The main side effects are diarrhoea, dry mouth and sometimes sleepiness. Very little else in normal doses.”
Professor Michael Heinrich, an ethnopharmacologist at the UCL School of Pharmacy, says “there are surprisingly few reported side effects” to CBD. Nevertheless, Prof Heinrich doesn't rule them out, explaining that, because most CBD is bought in a highly unregulated setting, it is “very unlikely any unforeseen effects will be recorded, as long as CBD is not covered under the Yellow Card scheme.” He believes it is unlikely, once significant controlled testing has been done, that CBD will have a dramatic level of side-effects.
Both professors agree there is a considerable issue around regulation. CBD is currently sold as a food substance, rather than as medicine (due to a paucity of evidence) so manufacturers cannot make health claims. It also means there can be a wide discrepancy in product quality.
Research in 2019, analysing 30 products on the market, found almost two-thirds contained less than 90 per cent of the declared CBD; many contained more. Almost half had traces of THC, so they were technically illegal, while one £90 item contained no CBD.
“I think there is an issue with the public not knowing exactly what they are getting from some products (though not all by any means). Having said that, the doses used are very low compared to, say, Epidiolex, and they are very safe. There is no evidence at all of liver problems in over the country products,” said Prof Barnes. Prof Heinrich agreed, stating that the main problems around CBD currently are that it's an unregulated market, meaning quality remains “a serious issue”.
Stephanie Price, editor of the Medical Cannabis Network, said: “Research on cannabis has been, and still is, constrained due to the scheduling of cannabis in the UK, and the review of research from the Committee of Toxicity rightly highlights that better research is needed.
“Although some studies have shown that CBD can present a risk to livers, for examples, CBD oil is still a low risk product. Keep in mind, supplements like vitamin D can be toxic if too much is taken. It is important in cases such as this to maintain a balanced perspective and not to over-exaggerate the dangers associated with such medicines.”
Last year, pharmacists were encouraged to monitor the safety of cannabis oil products after some were found to contain THC. In response to the review, a National Pharmacy Association spokesperson said: “In the case of CBD products, pharmacists should take account of current Home Office guidance, although it must be said the current guidance is difficult to interpret. We would welcome clear, authoritative guidance that makes it easier for manufacturers, health care professionals, retailers and consumers to make informed choices, keeping everyone on the right side of the law and safe from harm.
“For anyone thinking about buying such products, we'd suggest you first talk with your pharmacists about what is concerning you, and any symptoms you have, rather than ask about a specific product. The pharmacist might then be able to help you by supplying a suitable medicinal product, or give you the reassurance that you don't need to buy any products at all.”
Prof Barnes says the studies were done on “high, pure CBD”, and insists products found in health stores and pharmacists are “very safe”.