What is the risk of dependence in medical cannabis patients?

Researchers in the UK are exploring the risks of developing dependence among medical cannabis patients.

Recreational users have an estimated 8.9 percent chance of developing cannabis dependence, but experts argue that the same data cannot be applied to medical cannabis patients.

New research from Drug Science, the leading independent scientific body on drugs in the UK, highlights the differences between recreational and medical cannabis use to evaluate the risk of dependence.

Cannabis use disorder has been widely studied in recreational users, with these findings often projected onto medical cannabis patients.

In a review of the existing evidence, published in February, the team highlights the need for more studies investigating dependency specifically in people using cannabis for medical purposes.

For recreational users, the estimated chances of becoming dependent on cannabis after any lifetime exposure is considerably lower than for cocaine (20.9 percent), alcohol (22.7 percent) or tobacco (67.5 percent).

However, the United Nations reports that cannabis dependence is now the primary reason for drug treatment across the world (39 percent), surpassing numbers receiving opioid treatment (33 percent).

While the lines between recreational and medical use are “blurred at best” they argue, with many recreational users also self-medicating to manage symptoms of anxiety, for example – a number of factors need to be taken into account.

Dose and frequency of use are also key issues with the potential for medical cannabis dependence.

As a standard dose of cannabis does not exist, the patient rather than the doctor determines the correct dose and is required to titrate their dose to their desired effect.

This means medical patients often are titrating up to a higher dosage than recreational cannabis users, as they medicate throughout the day.

However, this does not necessarily put them at greater risk of dependence, argues lead author, Dr Anne Schlag, head of research at Drug Science.

“While overall medical cannabis users tend to use more frequently and more often daily than recreational users, on the other hand, medical users have less interest in getting ‘high’ and in having high THC products,” she says.

Long-term use of high-potency cannabis has been linked to dependence and mental health issues.

Dr Schlag continues: “In addition, early onset of use is also associated with dependence, but medical cannabis patients are usually a bit older at first time of use.”

How cannabis is consumed also has a role to play, with smoking the most common route of administration among recreational users, but not recommended for medical use, where vaporisers are often used as an alternative.

A 2018 study found higher THC concentrations in the blood following vaporisation compared to smoked cannabis, suggesting vaporising may lead to stronger effects than smoking.

Severe depression may also be a possible risk factor for dependence among chronic pain patients – the most common group of medical cannabis consumers – as mental health issues such as depression and anxiety are often associated with the condition.

But Drug Science researchers argue that it is important to put this into context.

Although medical cannabis may lead to dependence, it compares favourably, they say, in regards to other commonly prescribed drugs, such as opioids.

“Whilst there is a dependence risk associated with frequent cannabis use, current research from the US also indicates that some pain patients for example are able to decrease their opioid usage as a result of their medical cannabis use so it is important to contextualise findings,” says Dr Schlag.

“I am keen to see more research on if – and how – medical cannabis use is correlated with decreased prescription opioid use. Initial research in this area looks promising but more long-term data is needed.”

As access to medical cannabis improves, more research needs to be done into how dependence is measured in patients, adds Dr Schlag.

“Studies exploring medical cannabis dependence are scarce and the appropriate methodology to measure this construct is uncertain,” she says.

“We certainly require more studies addressing issues related to medical cannabis dependence specifically.

One move towards this is the new Cannabis-Based Medicines Questionnaire (CBM-Q) developed by Professor Val Curran, Dr Chandni Hindocha and other experts at Drug Science.

The questionnaire, which will be utilised in Project Twenty21 – the UK largest body of medical cannabis patients – aims to specifically address problematic medical cannabis use in a high number of respondents over a long period of time.

It will assess potential links to predisposing factors, such as underlying medical conditions.

“Many questions about the potential for medical cannabis use to lead to dependence remain to be answered,” adds Dr Schlag.

“It is imperative to address these questions in order to be able to minimise harms of medical cannabis use.”

Read the full report here and find out more about Project Twenty21 at www.drugscience.org.uk