Women are being ‘let down’ by research on cannabis because scientists only gear their studies towards men, experts claim.
Two drug researchers reviewed years of scientific literature behind the drug’s link with psychosis, which can drive patients to suicide.
In a damning verdict, they said ‘we are still not in a position to say cannabis causes psychosis’ – despite decades of costly research.
And they found a ‘gender bias’, warning the link between psychosis and cannabis in women is currently a mystery because of a lack of studies.
Two experts reviewed years of scientific literature behind the drug’s prominent link to the mental health condition, which can drive patients to suicide
Ian Hamilton, who led the study and is based at York University, told MailOnline: ‘Research is letting women down.
‘We should be spending research money on improving the information we have about the risk women face when using cannabis.
‘The research to date is completely biased towards men, a situation not helped by mainly men being in control of this research.’
The research of existing literature, published in Current Psychiatry Reports, was a review of dozens of scientific studies.
A substantial body of research, dating back a century, already exists to link smoking cannabis to psychosis, which often causes hallucinations.
But the review suggested the evidence for cannabis acting as a causal factor for the condition ‘has so far not been established’.
Mr Hamilton, who conducted the review of literature with Mark Monaghan from the University of Birmingham, said: ‘Research needs to extend beyond males.’
He warned no knowledge over the link between cannabis and schizophrenia will be gained unless experts start to include women in their studies.
Defending previous studies, Mr Hamilton said: ‘For researchers its a lot of easier to get people in treatment because they are already there.
‘But the problem of doing that is there is more men in treatment than women, so this is also added to this distorted view of cannabis and psychosis.
‘We don’t know enough about young women.’ He added it would be ‘remarkable’ if they were immune from the risk of psychosis.
‘I think a lot of money has been wasted replicating research that keeps trying to find and pin down a causal relationship between cannabis and psychosis,’ he said.
‘But it’s never going to happen. It’s too complicated. Instead, money should be spent on finding out the proportion of women who are at risk.’
Mr Hamilton said it is ‘clearly important’ that researchers investigate the risks for women not just men because of how many use the drug.
The British Crime Survey estimates that around one in 10 women use cannabis – the most widely used recreational drug in the world.
Possession of the class B drug carries an unlimited fine and up to five years in jail, while dealers face 14 years in prison.
What are the pros and cons of cannabis?
Cannabis is an illegal Class B drug in the UK, meaning possession could result in a five year prison sentence and those who supply the drug face up to 14 years in jail.
However, the drug is widely used for recreational purposes and can make users feel relaxed and happy.
But smoking it can also lead to feelings of panic, anxiety or paranoia.
Scientific studies have shown the drug can alleviate depression, anxiety and stress, but heavy use may worsen depression in the long term by reducing the brain’s ability to let go of bad memories.
It can also contribute to mental health problems among people who already have them, or increase users’ risk of psychosis or schizophrenia, according to research.
Marijuana can be prescribed for medical uses in more than half of US states, where it is used to combat anxiety, aggression and sleeping problems. Researchers are also looking into whether it could help people with autism,eczema or psoriasis.
Cannabis oil containing the psychoactive chemical THC, which is illegal in the UK, is claimed to have cancer-fighting properties, and one 52 year-old woman from Coventry says she recovered from terminal bowel and stomach cancer by taking the drug.
Discussing the gender bias, he told MailOnline: ‘In effect there are too many male researchers observing male cannabis users.’
Mr Hamilton added that, as a result of this, ‘we know very little about what the risks of psychosis are for women who use cannabis’.
He accepted that he knows his opinion sounds ‘obvious and daft’, adding too many senior researchers investigating cannabis are men.
Mr Hamilton said: ‘If you had some females in senior positions guiding research, they would bring a woman’s perspective to it.’
The NHS states cannabis is a drug ‘known to trigger psychotic episodes’. Others include cocaine, ecstasy and ketamine.
Powerful ‘skunk’ cannabis flooding the streets of Britain increases the risk of psychosis five-fold, a major study revealed in March.
The problem is so widespread that nearly a third of psychosis cases in London are caused by the drug, King’s College London researchers found
They warned that 94 per cent of all cannabis available on the streets of the capital is now in the form of skunk – purposely grown to have a high THC content.
Voices are growing for cannabis to be legalised in Britain, mainly driven by the Government’s decision to make it available medically last year.
Some supporters, including former deputy prime minister Sir Nick Clegg, believe making mild forms of the drug legal would stop people buying THC-abundant skunk.
But studies have suggested the potency of strains in Canada and the US, where cannabis is legal in some parts, has actually increased.
Mr Hamilton was behind research in 2017 that suggested the risk of developing psychosis as a result of smoking cannabis is much lower than first thought.
But he said the studies clearly showed that the stronger the weed, the more likely someone is to develop mental health problems.
Should cannabis be LEGAL? Experts are split on radical drug reform
Harry Sumnall, Professor in Substance Use, Liverpool John Moores University, advocated careful steps toward regulation as a public health policy
FOR: Harry Sumnall, Professor in Substance Use, Liverpool John Moores University
‘Cannabis is no ordinary consumer good, and as it has the potential to cause harm to users it should be carefully regulated by the state and not left in the hands of criminals.
‘If the government decided it wanted to begin the process of legalisation, it could first decriminalise use – removing criminal penalties and treating possession as we would a parking ticket.
‘After careful evaluation to ensure harms in vulnerable groups such as young people had not increased, full legalisation could begin.
‘We must learn from past mistakes made with alcohol and tobacco.
‘Promoting public health should be the priority of any model of cannabis regulation, and it is better to start off with tight restrictions that could be loosened.
‘For example, there should be age limits, a ban on advertising, and strict licensing of growers and retailers, with penalties for breaking rules.
‘Just because cannabis becomes legal doesn’t mean that we shouldn’t discourage use and help those who develop problems. Taxes raised from sales should be used to fund drug education and treatment.
‘Cannabis legalisation is a radical policy. It is better to be cautious and introduce changes in stages rather than be radical and regret things later.
AGAINST: Mark Winstanley, Chief Executive of Rethink Mental Illness
‘We welcome public debate of the role and impact of cannabis.
‘It’s important to distinguish between cannabis for medical use and recreational cannabis.
‘Where, there is clear evidence that it has a medical benefit we urge the Government to act to minimise unnecessary suffering.
‘However, we urge that we approach the legalisation of recreational cannabis with caution.
‘There is evidence of a link between recreational cannabis, particularly high potency forms, and psychosis and it is vital that this is a part of the debate.
‘It can be too easy to view all cannabis as ‘harmless’ when there can be very serious consequences.
‘We need to see more evidence from countries that have legalised cannabis on its effects on public mental health.
‘Currently things are inconclusive and a greater understanding is needed before action is taken.’
Rethink’s Mark Winstanley called for more understanding before any action is taken