The physicist Richard Feynman has been popularly quoted as stating that 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. More than 100 of these are cannabinoids: when ingested, they interact with a naturally occurring communication network in our brains and bodies 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, including gastrointestinal function, appetite, pain, memory, movement, immunity, inflammation and mental health.

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 pigeonholed as strictly helpful or harmful. Instead, meaningful discussion about its potential benefits and harms requires careful and nuanced consideration of the scientific literature, coupled with a humble attitude. As delineated in a recent and thorough review paper in the International Review of Psychiatry, the relationship 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 sense this intuitively: they will tell you that cannabis can help with their depressive symptoms. But there have been no randomized controlled trials to date that support the use of the cannabis plant or particular cannabinoids in the treatment of depressive disorders.

Further, and perhaps counterintuitively to some people, the scientific data that do exist are mixed and actually tilt 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 similarly confusing picture has been painted by the scientific literature for other psychiatric conditions. For example, two of the best-known 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: potency levels; the presence of other cannabis-related chemicals; the amounts used; and the person’s frequency of use, prior experience with the substance and ability to titrate the dose, 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 many factors.

The story about cannabis and addiction is no less confused. The scientific literature supports the idea that cannabis addiction is possible for a substantial minority of users, with THC’s euphoric effects thought to account for the addictive potential. This means that while a mere one in 10 people who ever try cannabis at least once might develop an addiction, this still represents a very large number of people.

The topic of cannabis and addiction has been turned on its head in recent years as cannabis has entered the discussion as a treatment for addictions to other substances—most notably opioids. If the goal of treatment is to reduce harm, it certainly makes sense to offer cannabis to replace opioids. But there is a line of thinking that cannabis treatment for other substance addiction holds promise not just for harm reduction but also as a treatment for addiction symptoms per se, such as withdrawal and cravings. The few studies that have been done have supported the rationale and funding of future research into this topic. This is exciting. It engenders hope. And yet, the beast of addiction is even more complicated than cannabis itself. It is therefore likely the case that while cannabis-based medicines can play a helpful role in the treatment of addiction, they will not be the solution. The causes of addiction are multifaceted and the solutions will continue to be multipronged.

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 the current ambiguity means you must be bound to current treatments.

For the occasional user, cannabis is relatively safe. It 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 it is to be used as part of a psychiatric treatment plan, then there is an ethical imperative to develop such a 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 disregarded, which could result in a worsening of mental health and addiction symptoms.

Additionally, from a psychological perspective, a person’s motive behind cannabis use matters. Research has shown that when people use the substance to escape from uncomfortable emotions, they can experience difficulties with mental health and addiction. Acutely mind-altering substances such as high-THC cannabis products can, in behavioral psychology language, be both positively reinforcing and negatively reinforcing.

In simpler language, this means that cannabis can reward by enhancing positive feelings and can also be relieving insofar as it can almost immediately take away the experience of uncomfortable emotions. But evidence-based psychological treatments of many psychiatric conditions involve the learning of 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 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.

Mixed messages about cannabis have become more common over time. This is not surprising given the 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. When it comes to mental health and addiction, we cannot afford to be blinded by ideology and lazy thinking.