Inside the Study Linking High-THC Consumption with Hidden Risks in Cannabis Patients

Researchers from King’s College London recently published the first findings from the Cannabis & Me study, which is said to be the largest investigation yet into how and why people across the UK use cannabis.

The general population survey included responses from over 3,000 people over the age of 18, who self-reported current or past cannabis use, some of whom were prescribed it through private clinics.

The researchers, led by Dr Edoardo Spinazzola, a Research Assistant at King’s IoPPN, examined their reasons for first and continued cannabis use, their weekly consumption of cannabis, and their mental health. Anyone diagnosed with a clinical psychotic illness was excluded from the study. 

“What we wanted to understand was whether the reason people start using cannabis for the first time has any sort of prediction on how much they end up using,” study co-author, Dr Marta Di Forti, Professor of Drug use, Genetics and Psychosis at King’s College London, explained in an interview with Cannabis Health.

“And in turn, whether this has any impact on outcomes such as paranoia.”

The majority of people in the survey reported beginning cannabis use in their teens for fun, out of curiosity, or with friends, and their use was only occasional. However, over 400 participants said they began using cannabis to relieve discomfort, whether psychological, such as anxiety or low mood, or physical pain.

Respondents who first started using cannabis to self-medicate an illness, including physical pain, anxiety, depression, or because they were experiencing minor psychotic symptoms, all demonstrated higher paranoia scores, Di Forti says, close to what would be considered a “clinical threshold”.

This group, the researchers found, not only used cannabis more frequently but also consumed higher levels of THC, which in turn was associated with greater levels of paranoia among participants.

Using a standardised THC unit, developed by Professor Tom Freeman, Director of the Addiction and Mental Health Group at the University of Bath, the researchers found that the average respondent consumed 206 units of THC a week. 

This would equate to roughly 10-17 ‘joints’ per week, if the user was consuming an expected 20 per cent THC content that is standard for the most common types of cannabis available in London.

Respondents who started using cannabis to help with their anxiety, depression, or in cases where they started due to others in their household who were already using cannabis, reported on average 248, 254.7, and 286.9 average weekly THC units, respectively.

“If you are trying to ameliorate a discomfort that can be psychological or pain… this is a group that is more likely to use daily and to end up consuming higher-concentration THC,” Di Forti said. 

A separate study, also using data from the Cannabis & Me project, led by psychiatrist Dr Giulia Trotta, explored another important variable. 

Childhood trauma, Di Forti explains, “is one of the strongest predictors of paranoia,” and also increases the likelihood of using cannabis in the first place.

Researchers used the same data set, with just over half of respondents (52 per cent) reporting experience of some form of trauma. They found that those individuals were more likely to use cannabis and to consume higher levels of THC, but when trauma and heavy cannabis use occurred together, paranoia rose sharply. 

“It’s what we call an interaction between two factors that independently have an impact on paranoia,” Di Forti says. 

“When you put them together, things are much worse.”

The researchers concluded that the strong association between childhood trauma and paranoia is further exacerbated by cannabis use, but it is also affected by the different types of trauma experienced. 

Respondents who said they had experienced emotional abuse or household discord were strongly associated with increased THC consumption and paranoia scores. Meanwhile, respondents reporting bullying, physical abuse, sexual abuse, physical neglect and emotional neglect, on the other hand, did not show the same effects.

“The outcome is that if you have experienced trauma, and you feel that using cannabis is a way to relieve the negative emotions, be aware that these actually are shown in the long-term, to make things worse,” says Di Forti.

“Many people who use cannabis don’t develop psychosis, but if you add other risk factors, which can be trauma or discrimination, then you could push them over the threshold. I think that’s the bottom line: If you have trauma, because of the relationship between trauma and paranoia, please don’t add cannabis on top of it. Perhaps you can consider other types of support which don’t have to be medication, such as psychological therapy.”

According to Di Forti, around two-thirds of those surveyed in the group described as ‘self-medicating’ were prescribed legal cannabis products through private UK clinics, meaning the outcomes could not be explained by “contaminated cannabis”.

“As far as we believe, all legal cannabis clinics have reputable products, and there is a degree of quality control,” she says.

“It’s just that in the end, they were using too much.”

These vulnerabilities, Di Forti adds, highlight why the right clinical oversight is crucial for patients using cannabis therapeutically. Tens of thousands of patients are now prescribed medical cannabis products through private clinics in the UK, but she has concerns about a “lack of protocols” and “inconsistency” in practices. 

“Once you have got an initial prescription, you don’t necessarily need to see a physician again to get a repeat,” she says.

“There is a huge variability between the clinics in terms of when this is required, and this lack of consistency and protocol exposes potentially vulnerable people.” While clinics may monitor physical side effects like nausea or dizziness, psychological effects such as paranoia are much harder to identify. 

“Understanding if you become paranoid is not like noticing you’ve got tummy pain,” Di Forti explains. 

“It’s an insidious process. By the time it becomes disabling, you might not have made any connection to the THC.”

Di Forti, who runs The Cannabis Clinic for Patients with Psychosis in London, says that while there is no official data, she and other colleagues in psychiatry have reported cases of patients being diagnosed with psychosis after having consumed high-THC products prescribed to them through UK clinics.

“These are just anecdotes,” she stresses. 

“We need more data to be published, to be able to see at which level this group of people is actually reaching clinical services.” 

But the research is not about “condemning the medical use of cannabis”, Di Forti insists.

She has welcomed recent Phase III studies which show a cannabis-derived drug to be effective in managing chronic lower back pain, as “very promising”. But she argues that more of these advanced trials are needed so clinicians know what conditions it should be prescribed for, and at what dose or concentration.

“The message is not that people shouldn’t seek to ameliorate that discomfort, and indeed, studies like these show that there are cannabis compounds that are beneficial for pain, for instance,” she adds.

“The message is, that if you’re using cannabis because you’re trying to feel better, do it with some support and monitoring, to make sure that you are using a preparation of cannabis which is the right balance and the right concentration, particularly of THC… and make sure that you are not using something that is going to cause other concerns.”