The esteemed physicist Richard Feynman has been popularly quoted as saying: If you think you understand quantum mechanics, then you don’t understand it. Maybe it’s not a quantum leap to make the same claim about cannabis.
The cannabis plant is not a single substance, but contains more than 500 identified chemical components, of which more than 100 are chemicals called cannabinoids that, when ingested, interact with a natural communication network throughout our brain and body known as the endocannabinoid system. As a result, different permutations and dose combinations of cannabis can affect many physiological and psychological processes in different ways, such as gastrointestinal function, appetite, pain, memory, movement, immunity, inflammation and mental health.
The exciting news about the complexity of cannabis is that it holds great promise as a potential drug for many diseases. The disturbing news is that there is a gap between the hype and the evidence-based research that supports the hype. This concern is particularly true with regard to the issue of mental health, in which cannabis has been promoted in the popular media as an effective treatment for a variety of psychiatric conditions, including depression, anxiety, post-traumatic stress disorder, psychosis and addiction.
The reality is that cannabis cannot be pigeonholed into strictly useful or harmful categories. The complexity of cannabis does not allow claims about its effects to be watered down and distilled into incomplete truths. On the other hand, a meaningful debate about the possible benefits and harms of cannabis requires a careful and nuanced review of the scientific literature, along with a humble attitude. As outlined in three recent studies – one in the International Review of Psychiatry, one in The American Journal on Addictions and one in The Lancet Psychiatry – the relationship between mental health status and cannabis status is particularly complicated.
For example, with regard to depression, the science is clear that the endocannabinoid system plays a role in regulating mood. Some people may know this intuitively because people will tell you that cannabis can help with their depressive symptoms. That said, to date, support for the use of the cannabis plant or certain cannabinoids in the treatment of depressive disorders and symptoms is limited. In addition, and perhaps in a contradictory way for some people, the existing scientific data are mixed and in fact inclined towards the idea that ingested cannabis plant material probably leads to the development and worsening of depressive symptoms. These results are not satisfactory. They are not simple. They suggest the possibility of developing cannabis-based drugs for depression, while warning 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-tetrahydrocannabinol (THC) and cannabidiol (CBD). In general, THC has been shown to produce anxiety and psychotic characteristics, especially at higher doses, while CBD has been shown to produce anxiolytic and antipsychotic effects. However, many other variables affect whether a person will experience greater or lesser anxiety or psychotic symptoms when ingesting cannabis, including the presence of other cannabis-related chemicals, potency levels and amounts consumed, as well as the frequency with which a person uses cannabis, previous experience with cannabis, his or her ability to assess his or her dose, coexisting medical conditions and his or her likelihood of experiencing psychiatric symptoms. Reflecting this complexity, the current state of scientific data on the use of cannabis for the treatment of post-traumatic stress disorder symptoms is also mixed, so cannabis has been shown to have useful and harmful effects depending on a range of cannabis-related and human factors.
The story about cannabis and addiction is no less telling. A review of the scientific literature supports the idea that cannabis addiction is possible for a substantial minority of users, so the euphoric effects of THC are believed to explain the addictive potential of cannabis. This means that while approximately 1 in 10 people who try cannabis at least once may develop a cannabis addiction, this percentage minority actually reflects the fact that cannabis is not a drug.