Cannabis may be behind a surge in schizophrenia cases, alarming research suggested today.
Advocates of the drug often purport that marijuana is safe because it is ‘natural’.
But Canadian researchers found new cases of schizophrenia triggered by cannabis have tripled since the country legalised the drug in 2015.
In just under two decades, the figure rose from 4 per cent to over 10 per cent, the scientists said.
Experts warned the findings show that using the drug also heavily worsens symptoms of the condition and that cannabis poses a ‘growing public health challenge’.
Dr Daniel Myran, an expert in public health and preventative medicine at the University of Ottawa and study co-author, said: ‘Regular cannabis use is strongly associated with an increased risk of schizophrenia.
‘The tripling of schizophrenia cases associated with a cannabis use disorder over the past 17 years and rising cases of psychosis underscores the urgent need for targeted prevention strategies, particularly for younger populations who appear to be at the greatest risk.
‘Our study highlights the growing public health challenge posed by the combination of increasingly high-potency cannabis and rising regular cannabis use.’
Canadian researchers found new cases of schizophrenia triggered by cannabis have tripled since the country legalized the drug in 2015
In the UK, laws around the medical use of cannabis were relaxed almost seven years ago.
It is available on the NHS under strict guidelines to help control seizures, for chronic pain and to those with the degenerative condition multiple sclerosis — however, just 110 prescriptions have been issued in the past five years.
But in Canada, medical cannabis was legalised in 2015 and non-medical cannabis use in 2018.
In the study, the researchers tracked the number of residents aged 14 to 64 in Ontario, southern Canada who visited the emergency department between 2006 and 2022.
Over the follow-up of 17 years, 10,583 with cannabis use disorder (9 per cent) developed schizophrenia compared to 80,523 (0.6 per cent) of individuals without.
Writing in the journal JAMA Network Open, the scientists said: ‘Consistent with increasing cannabis use and potency, emergency department visits in Ontario for cannabis induced psychosis and cannabis use dependency have increased over time.
in Canada , medical cannabis was legalised in 2015 and non-medical cannabis use in 2018
‘The association between cannabis use disorder and schizophrenia may be particularly elevated among younger males.’
They also found the number of people who required hospital care for cannabis use disorder — addiction to the substance — rose 270 per cent since before legalisation to after the legalisation of non-medical cannabis.
Over the same period, the percentage of all new cases of schizophrenia who had received hospital care for the disorder before their diagnosis increased from 7 to 16 per cent.
It comes as NHS figures last month found a record number of older Brits were hospitalised after smoking cannabis last year amid a surge in ‘silver smokers’.
More than 2,700 adults aged 65 and older — including 9 over 90s — were admitted to hospital in England between April 2023 and March 2024 suffering adverse reactions or overdoses.
It marks a rise of 56 per cent on pre-pandemic levels and a staggering 650 per cent on a decade ago.
Patients reported experiencing hallucinations, withdrawal symptoms and even suffering cannabis poisoning.
Separate annual figures from the Office for National Statistics show cannabis remains the most popular drug among 16 to-59-year-olds in England and Wales.
Use was highest among 20 to 24-year-olds last year, official figures show.
Just over a quarter of all young adults quizzed between April 2023 and March 2024 said they had ever smoked weed in their lifetime.
Last year, private cannabis prescriptions doubled — reaching nearly 180,000 — according to the Care Quality Commission (CQC).
Meanwhile in the US, the drug has seen a meteoric rise over the past decade, culminating in legal recreational use in 24 states.
THC — one of the main active components found in marijuana — stimulates areas of the brain involved with mood, attention and memory, while triggering the release of the hormone dopamine, responsible for feelings of reward and pleasure.
Small, infrequent doses have little long-term impact, according to studies.
But with prolonged, regular use, signals in these key brain areas can start to go awry.
Studies have suggested that frequent cannabis use can increase the risk of serious mental illness like schizophrenia, as well as insomnia, social anxiety disorder and suicidal thoughts.
The cause of schizophrenia is not understood and it is believed to be a mix of genetics, abnormalities in brain chemistry and/or possible viral infections and immune disorders.
Symptoms of schizophrenia usually begin between ages 16 and 30. They include hallucinations, muddled thoughts and speech and wanting to avoid people.
Figures suggest around 1 per cent of the world population suffers from schizophrenia, including around 685,000 in the UK and two million in the US.
Article by:Source:
