The researchers have reviewed a total of 83 studies published over the past 40 years - and believe that the risks of treating mental illness with medical cannabis today outweigh the benefits.
They also highlight the fact that you still treat mental illness with cannabinoids in several parts of the world despite the need for more qualitative studies to determine what may or may not work.
"Before we have evidence from randomized controlled trials, we can't provide clinical advice on how medical cannabis can be used to treat mental illness," says study lead author Louisa Degenhardt.
Small positive effect
The researchers looked at what we know about medical cannabis to treat depression, anxiety, ADHD, Tourette's syndrome, post-traumatic stress disorder, (PTSD) and psychotic illness.
However, a small positive effect on anxiety relief could be seen in patients suffering from multiple sclerosis or chronic pain. Here, however, the effect on anxiety could have to do with cannabis providing pain relief, which in turn reduced anxiety symptoms.
In addition to the researchers finding that the evidence about medical cannabis was slim, the findings in the study indicate that cannabis can increase the incidence of depression, anxiety and psychotic symptoms.
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Cannabis - more dangerous than you think? Photo: SVTNot enough studies have been done
Amir England is a cannabis researcher at King's College in London. He thinks the new meta-analysis is interesting and that the main message is that not enough studies have been done on the subject.
- It is possible that cannabis substances may be effective for mental disorders, but at the same time not. Not enough good studies have been done for us to know.
- But interest in researching cannabis has increased worldwide and we have several ongoing or planned studies that will contribute knowledge in the future.