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Is Cannabis Helpful or Harmful for Mental Health?

The evidence suggests that it's complicated.

The esteemed physicist Richard Feynman has been popularly quoted as stating: If you think you understand quantum mechanics, then you don’t. It is perhaps not a quantum leap to make the same claim about cannabis.

The cannabis plant is not a single substance, but rather contains more than 500 identified chemical constituents, of which more than 100 are chemicals called cannabinoids that when ingested, interact with a naturally occurring communication network throughout our brain and body known as the endocannabinoid system. As a result, varying permutations and combinations of cannabis dosages can affect many physiological and psychological processes in different ways, such as gastrointestinal function, appetite, pain, memory, movement, immunity, inflammation, and mental health.

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The exciting news about the complexity of cannabis is that it holds much promise as a potential medicine for many ailments. The worrisome news is that there is a gap between the hype and the evidence-based research supporting the hype. This worry is particularly true with respect to the topic of mental health, whereby cannabis has been touted in popular media as an effective treatment for a variety of psychiatric conditions, such as depression, anxiety, post-traumatic stress, psychosis, and addiction.

The reality is that cannabis cannot be pigeon-holed into strictly helpful or harmful categories. The complexity of cannabis does not allow for claims about its effects to be cheapened and distilled to incomplete truths. Instead, meaningful discussion about the potential benefits and harms of cannabis requires careful and nuanced consideration of the scientific literature coupled with a humble attitude. As delineated in three recent thorough review papers—one in the International Review of Psychiatry, one in The American Journal on Addictions, and one in the Lancet Psychiatry—the relationship status between cannabis and mental health is especially complicated.

For example, with respect to depression, the science is clear that the endocannabinoid system plays a role in mood regulation. Some people might know this intuitively because people will tell you that cannabis can help with their depressive symptoms. That said, to date, there is limited support for the use of the cannabis plant or particular cannabinoids in the treatment of depressive disorders and symptoms. Further, and perhaps counterintuitively to some people, the scientific data that does exist are mixed and actually tilted towards the idea that ingested cannabis plant material likely leads to the development and worsening of depressive symptoms. These findings are not satisfying. They are not straightforward. They suggest the possibility of the development of cannabis-based medicines for depression while simultaneously cautioning against the self-medicated use of cannabis for depression.

A similar confusing picture has been painted by the scientific literature for other psychiatric conditions. For example, two of the most famous cannabinoids found in the cannabis plant are delta-9-tetrahydrocannabinold (THC) and cannabidiol (CBD). In general, THC has been shown to produce anxiety and psychotic features, especially at higher doses, whereas CBD has been shown to produce anxiolytic and antipsychotic effects. However, many other variables affect whether a person will experience increased or decreased anxiety or psychotic symptoms when ingesting cannabis, including the presence of other cannabis-related chemicals, potency levels, and amounts used, as well as how frequently a person uses cannabis, their prior experience with cannabis, their ability to titrate their dose, co-occurring medical conditions, and their likelihood to experience psychiatric symptoms. Mirroring this complexity, the current state of the scientific data for the use of cannabis in treating post-traumatic stress disorder symptoms are also mixed, whereby cannabis has demonstrated both helpful and harmful effects depending on a number of cannabis-related and person-related factors.

The story about cannabis and addiction is no less relenting. A perusal of the scientific literature supports the idea that cannabis addiction is possible for a substantial minority of users, whereby THC’s euphoric-producing effects are thought to account for cannabis’ addictive potential. This means that while approximately 1 in 10 people who ever try cannabis at least once might develop a cannabis addiction, this percentage-wise minority actually reflects an absolute large number of people given the widespread use of cannabis.

The topic of cannabis and addiction has turned on its head in recent years as cannabis has entered the discussion as a treatment for other substance addictions, most notably opioid addiction. If the goal of treatment is to reduce the harm that a person experiences, it certainly makes sense to offer cannabis in the hopes that more harmful substance use decreases. But there is a line of thinking that cannabis treatment for other substance addiction holds promise for more than just harm reduction and can serve as treatment for addiction symptoms per se, such as withdrawal and cravings. The few studies that have been conducted have supported the rationale and funding of future research into this topic with respect to opioid addiction. It is exciting. It engenders hope. And yet, the beast of addiction is more complicated than cannabis itself, and it is therefore likely the case that cannabis-based medicines might play a helpful role in the treatment of substance addiction but will not be the solution. The causes of addiction are multifaceted and the solutions will continue to be multi-pronged.

How is one to navigate this mess, both as a consumer and medical professional? Well, if you happen to not care what the evidence says, then Godspeed. But if you believe in evidence-based science and practice, then it looks like in most cases, you are likely paralyzed by indecision on how to proceed at the present time and are bounded to the current gold-standards of treatment. Indeed, the recent review article in the Lancet Psychiatry concluded, “There remains insufficient evidence to provide guidance on the use of cannabinoids for treating mental disorders within a regulatory framework.” That said, it might be argued that the current state of very poor quality cannabis-related research certainly highlights and challenges our notions and thresholds for what might be considered evidence-based medicine.

It is important to remember that for the occasional user, cannabis is relatively safe. Cannabis can be made even safer by following low-risk guidelines that have been developed by the research community. But for those with mental health and addiction concerns, cannabis can be both a friend and enemy. If cannabis-based medicines are to be used as part of a psychiatric treatment plan, then it is an ethical imperative to develop this plan in consultation with a treatment team that practices evidence-based medicine. One risk of self-medication with cannabis is that other evidence-based treatments could be neglected, which could result in a worsening of mental health and addiction symptoms.

Additionally, from a psychological perspective, a person’s motive or the intention behind their cannabis use matters. Research has shown that when people use cannabis to escape from uncomfortable emotions, they can experience difficulties with mental health and addiction, as well as problems associated with their cannabis use. The reason for this phenomenon is refreshingly uncomplicated. Acutely mind-altering substances such as high-THC cannabis products can, in behavioural psychology language, be both positively reinforcing and negatively reinforcing. In simpler language, this means that cannabis can be rewarding by enhancing positive feelings and it can also be relieving insofar as it can almost immediately take away the experience of uncomfortable emotions. Evidence-based psychological treatments of many psychiatric conditions involve learning skills to confront and engage with difficult emotions, not avoid them. If cannabis is being used to avoid uncomfortable emotions, thoughts, and memories, then it can lead to the development or worsening of psychiatric symptoms. In other words, repeated temporary relief from psychiatric symptoms by using acutely-mind altering substances is not therapy, and in fact, often runs counter to therapy because it robs the brain of the opportunity to practice healthy coping skills.

Mixed messages about cannabis have become the rule rather than the exception. This is not surprising. These mixed messages reflect the reality and complexity of the cannabis plant and the complexity of conducting cannabis-related research. The irony of discussions surrounding cannabis is that they are often so emotionally- and politically-charged that they become polarized in a way that completely belies the intricacies and weight of the topic. When it comes to mental health and addiction, we cannot afford to be blinded by ideology, lazy thinking, and tribal affiliations in a cannabis culture war.

A version of this article was originally published by Scientific American.

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