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There is no scientific evidence that medical cannabis is effective at treating people with mental health conditions, research shows.
Australian scientists reviewed 83 studies involving 3,000 people to come to their conclusion. They found no proof cannabinoids relieved the symptoms of six disorders – depression, anxiety, ADHD, Tourette syndrome, PTSD or psychosis.
Therefore the use of medicinal cannabis for mental health problems cannot be justified based on the current evidence, they concluded. This is due to a lack of evidence for their effectiveness, and because of the known risks.
Cannabis use, particularly strains with high THC content, increases your risk of developing a psychotic illness such as schizophrenia. And for an estimated one in 10 cannabis users who become addicted, it can cause withdrawal symptoms such as anxiety and insomnia.
THC is the main psychoactive compound in marijuana which gives users a high and can also trigger anxiety in some smokers. CBD, on the other hand, is thought to be responsible for some therapeutic effects of cannabis, such as pain relief and relaxation.
Medical cannabis has been shown to treat a host of conditions including arthritis and MS, as well as in patients who suffer chronic seizures. But the new findings, published in The Lancet Psychiatry journal, found insufficient evidence medicinal cannabinoids improves mental health problems overall or their symptoms.
They did however note a small improvement in anxiety in individuals with other medical woes, such as chronic pain or multiple sclerosis. Around the world, cannabis is increasingly being made available for medicinal purposes, including for the treatment of mental health disorders.
Medicinal cannabinoids include medicinal cannabis, pharmaceutical cannabinoids, and their synthetic derivatives, THC and CBD.
HOW IS MEDICAL CANNABIS SAID TO WORK?
A broad term for any sort of cannabis-based medicine used to relieve symptoms. Some products that might claim to be medical cannabis, such as CBD oil or hemp oil, are available to buy legally as food supplements from health stores.
But there’s no guarantee these are of good quality or provide any health benefits. And some cannabis-based products are available on prescription as medicinal cannabis. These are only likely to benefit a very small number of patients.
Epidiolex for children and adults with epilepsy
Epidiolex is a highly purified liquid containing CBD (cannabidiol).
CBD is a chemical substance found in cannabis that has medical benefits.
It won’t get you high, because it doesn’t contain THC, the psychoactive chemical in cannabis.
Epidiolex is not yet licensed in the UK but is currently going through the licensing system.
In the meantime, the unlicensed medication can be prescribed for patients with Lennox-Gastaut syndrome and Dravet syndrome (both rare forms of epilepsy).
Nabilone for chemotherapy patients
Many people having chemotherapy will have periods where they feel sick or vomit.
Nabilone can be prescribed by a specialist to help relieve these symptoms, but only when other treatments haven’t helped or aren’t suitable.
Nabilone is a medicine, taken as a capsule, that has been developed to act in a similar way to THC.
The medicine has been licensed in the UK.
This means it has passed strict quality and safety tests, and is proven to have medical benefit.
Nabiximols (Sativex) for MS
Nabiximols (Sativex) is a cannabis-based medicine that is sprayed into the mouth
It is licensed in the UK for people with MS-related muscle spasticity that hasn’t got better with other treatments.
But its availability on the NHS is limited. The National Institute for Health and Care Excellence (NICE) does not recommend that NHS doctors prescribe Sativex, as it is not cost effective.
There is some evidence medical cannabis can help certain types of pain, though this evidence is not yet strong enough to recommend it for pain relief.
Lead author Louisa Degenhardt, professor in addictions at the University of New South Wales in Sydney, Australia, said: ‘Our findings have important implications in countries where cannabis and cannabinoids are being made available for medical use.
‘There is a notable absence of high-quality evidence to properly assess the effectiveness and safety of medicinal cannabinoids compared with placebo.
‘Until evidence from randomised controlled trials is available, clinical guidelines cannot be drawn up around their use in mental health disorders.’
She continued: ‘In countries where medicinal cannabinoids are already legal, doctors and patients must be aware of the limitations of existing evidence and the risks of cannabinoids.
‘These must be weighed when considering use to treat symptoms of common mental health disorders.
‘Those who decide to proceed should be carefully monitored for positive and negative mental health effects of using medicinal cannabinoids.’
As part of their analysis, the researchers looked at 83 published studies.
Forty of these were randomised controlled trials and the remaining 43 were open-label studies, where participants knew which treatment they were taking.
Of the 83 studies, 42 looked at depression, 31 looked at anxiety, eight looked at tourette syndrome, three were on ADHD, 12 were on PTSD, and 11 were on psychosis.
Few randomised controlled trials examined the role of CBD or medicinal cannabis – most looked at THC, with or without CBD.
The authors found that pharmaceutical THC improved anxiety symptoms among individuals with other medical conditions – in seven studies of 252 people.
However this may have been due to improvements in the primary medical condition, the researchers say.
They suggest further studies should explicitly study the effects of cannabinoids on anxiety and depression.
Pharmaceutical THC, with or without CBD, worsened negative symptoms of psychosis in one study of 24 people.
It did not significantly affect any other primary outcomes for the mental health disorders examined, they found.
THC also increased the number of people who had adverse events in ten studies involving 1,495 people compared with placebo across all six mental health disorders studied. The researchers say the review highlights the limited evidence and the low quality of the evidence that exists around using cannabinoids for treatment of mental health conditions.
Professor Degenhardt added: ‘Cannabinoids are often advocated as a treatment for various mental health conditions.
‘Countries that allow medicinal cannabinoid use will probably see increased demand for such use.
‘Clinicians and consumers need to be aware of the low quality and quantity of evidence for the effectiveness of medicinal cannabinoids in treating mental health disorders and the potential risk of adverse events.
‘Given the likely interest but scant evidence to guide patient and clinician decisions around cannabinoids for mental health, there is an urgent need for randomised controlled trials to inform whether there are benefits of cannabinoids for these indications.’
The authors highlight that their analysis and conclusions are limited by the small amount of available data.
They also note that most studies are based on pharmaceutical cannabinoids, rather than medicinal cannabis.
Ian Hamilton, a lecturer in addiction and mental health at the University of York, said: ‘On the face it of it this review appears to pour cold water on the claims made by patients and those selling cannabis products for mental health.
THE DIFFERENCES BETWEEN THC AND CBD
Tetrahydrocannabinol (THC) and cannabidiol (CBD) are both derived from the cannabis plant.
Together, they are part of the cannabinoid group of compounds found in hashish, hash oil, and most strains of marijuana.
THC is the psychoactive compound responsible for the euphoric, ‘high’ feeling often associated with marijuana.
THC interacts with CB1 receptors in the central nervous system and brain and creates the sensations of euphoria and anxiety.
CBD does not fit these receptors well, and actually decreases the effects of THC, and is not psychoactive.
CBD is thought to help reduce anxiety and inflammation.
‘The researchers looked for evidence more thoroughly than anyone has so far, they were unable to find anything that supports using these products for common mental health problems.
‘This will no doubt frustrate people who feel their mental health has improved having tried cannabis products, they may feel that their experiences are not being valued or listened to.
‘However while this review couldn’t find evidence for using cannabis that’s not the same thing as saying they are ineffective.
Professor Hamilton said there were two important factors to consider.
He added: ‘First the researchers point to a lack of trials investigating these products for mental health problems.
‘Secondly no-one is an average so it might be that these products don’t improve many people’s mental health but they do help some people, although the only way of knowing who these people are is if we let them try the products.
‘Unfortunately traditional medicines used to treat mental health problems can give people unwanted side effects and require patients to stay on them for some time.
‘Finding alternatives that have fewer side effects is clearly important. Also it might be that some patients view cannabis as a more natural compound when compared with synthetic traditional medicines.’
Dr Tom Freeman, lead director of the Addiction and Mental Health Group at the University of Bath, said the analysis strengthened the view that there is not enough evidence to prescribe medical cannabis to people with mental health conditions.
He added: ‘The quality of evidence is also low for the use of cannabinoids in the treatment of other medical indications, as outlined in draft recommendations by the National Institute of Health and Care Excellence (NICE).
‘Given the significant demand for access to these medications from patients, further research is urgently needed to strengthen the evidence.
‘The only way for patients to access these medications at present is through private prescription which require vastly excessive costs, or via the illicit market which carries risk of prosecution as well as unknown product content, quality and safety.’