Cannabis users at ‘much higher’ risk of developing poor mental health

Those with a recorded history of cannabis use in general practice records are at a much higher risk of developing mental ill health problems such as anxiety or depression as well as severe mental illnesses, new research shows.

The findings point to the need for a public health approach to the management of people misusing cannabis, including the need to emphasise the importance of general practitioners to continue enquiring about recreational drug use.

While the links between cannabis use and severe mental illnesses such as schizophrenia and psychosis are well researched, the associations are less clear between cannabis use as described in patient’s GP records and other, more common types of mental ill health such as depression and anxiety.

In a new study, published in Psychological Medicine, researchers in the University of Birmingham’s Institute for Mental Health and the Institute of Applied Health Research found a strong link between general practice recorded cannabis use and mental ill health in one of the largest cohorts ever explored.

Senior author Dr Clara Humpston said: “Cannabis is often considered to be one of the ‘safer’ drugs and has also shown promise in medical therapies, leading to calls for it be legalised globally. Although we are unable to establish a direct causal relationship, our findings suggest we should continue to exercise caution since the notion of cannabis being a safe drug may well be mistaken.”

Dr Joht Singh Chandan said: “The research reaffirms the need to ensure a public health approach to recreational drug use continues to be adopted across the UK. We must continue to progress measures to improve the prevention and detection of drug use as well as implement the appropriate supportive measures in an equitable manner to prevent the secondary negative health consequences.”

Using primary care data drawn from the IQVIA Medical Research Database (IMRD-UK) the researchers found following the first recorded use of cannabis, patients were three times more likely to develop common mental health problems such as depression and anxiety. In addition, they were almost 7 times more likely to develop severe mental illnesses such as psychosis or schizophrenia.

The dataset included records from 787 GP practices around the UK gathered over a 23-year period between 1995 and 2018. The researchers were able to include data from 28,218 patients who had a recorded exposure to cannabis. These were matched to 56,208 patients who had not been using cannabis and controlled for sex, age, ethnicity, smoking status and other relevant characteristics.

The cannabis users also had much higher rates of having a recorded history of using other drugs such as heroin, cocaine and amphetamines.

Future research in this area will investigate the levels of cannabis use or the potency of ingredients.

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Notes to editor:

• The University of Birmingham is ranked amongst the world’s top 100 institutions. Its work brings people from across the world to Birmingham, including researchers, teachers and more than 6,500 international students from over 150 countries.
• Keerthy et al (2021). ‘The associations between primary care recorded cannabis use and mental ill health in the UK: A population-based retrospective cohort study using UK primary care data’. Psychological Medicine.