Posted December 14, 2016 by Ljubica Kostovic

Cannabis and Mental Health


This week’s post is a guest submission by Michelle Thiessen. Michelle is a Master’s student in Clinical Psychology at the University of British Columbia, focusing on cannabis and mental health. She is also the Treasurer for Canadian Students for Sensible Drug Policy. 

Humans have been using cannabis to treat both physical and psychological concerns for thousands of years. However, in recent years cannabis research has predominantly examined the negative health consequences of illicit cannabis use. When compared with decades of negatively positioned research, there appears to be a relatively small number of contemporary studies looking into the potential mental health benefits of cannabis use.

Despite the low volume of research into the effects of cannabis on mental health, a substantial portion of medical cannabis users report treating their anxiety, mood disorders, and sleep problems with cannabis (Walsh et al., 2013).

Our lab at the University of British Columbia (UBC) recently conducted the most comprehensive review of cannabis use and mental health research to date. While cannabis may not be helpful for everyone, and in some cases may be harmful (e.g. for those with bipolar disorder and schizophrenia), we found that cannabis was helping some patients treat their depression and anxiety. We also reviewed a number of studies that pointed to cannabis as a potential treatment for post-traumatic stress disorder.

This finding is especially exciting given that we at UBC are currently undertaking the first Canadian clinical trial of cannabis for a mental health disorder focusing on the efficacy of three different cannabis “strains” (i.e. high CBD/high THC; low CBD/high THC; low CBD/low THC) for PTSD.


Post-traumatic stress disorder (PTSD) is a serious, worldwide public health problem which affects an estimated 9% of Canadians over the course of their lifetime (Langlois, Samokhvalov, Rehm, Spence, & Gorber, 2015). A recent epidemiological study found that 76% of respondents had been exposed a traumatic event sufficient to cause PTSD and the most common forms of trauma resulting in PTSD included the unexpected death of a loved one, sexual assault, and seeing someone badly injured or killed (Van Ameringen et al., 2008).

Post-traumatic stress disorder is characterized by an inability to recover from a stress reaction following exposure to a traumatic event (Kessler, Sonnega, Bromet, Hughes, & Nelson, 1995) and is defined as the non-remittance of symptoms of intrusion, avoidance, negative alterations in cognition and mood, and arousal and reactivity by 1-month post-traumatic event exposure (DSM-5; APA, 2013). Many PTSD sufferers experience a dramatic reduction in quality of life, debilitating sleep problems, and may withdraw from relationships because of the trauma and resulting symptoms.

Unfortunately, treatment is relatively ineffective for a sizeable amount of people that may spend the rest of their lives trying to simply manage their symptoms.
A range of psychotherapeutic and evidence-based treatment options exist for treating PTSD. However, a significant percentage of patients fail to respond to these established treatments (Brady et al., 2000; Resick & Schnicke, 1992) and because of the lack of clinically meaningful reductions in symptoms, researchers have begun to investigate alternative solutions.

Although the research is still in its infancy, evidence suggests cannabis may have salutary effects for PTSD treatment and retrospective reports of cannabis use have found reductions in PTSD symptoms following use (Greer et al., 2014). Cannabis-based medicines have demonstrated effectiveness for improving sleep quality and reducing nightmares. It’s estimated that half of PTSD sufferers experience distressing nightmares that have elements of the original trauma in them.

A study of combat veterans reported that cannabis use was associated with a 75% reduction in PTSD symptoms (re-experiencing, avoidance, arousal) compared with cannabis abstinent participants (Greer, Grob, & Halberstadt, 2014). In Canada, Veterans Affairs covers the cost of medical cannabis purchased to treat PTSD (although they have recently reduced the amount that they will cover).
Beyond treating the PTSD symptoms, other studies have looked at differential functioning of the endocannabinoid system in those exposed to chronic stress. Chronic stress has been shown to deplete the endocannabinoid system. A population-based cohort study of individuals with close proximity to the World Trade Center at the time of the 9/11 attacks found those that met criteria for PTSD had lower levels of the endogenous cannabinoid anandamide when compared to individuals not meeting criteria for PTSD (Hill et al., 2013). Animal studies have found that reductions in endogenous cannabinoids promote the retention of aversive emotional memories, a defining feature of PTSD.
Years of prohibition that resulted in barriers to research have undoubtedly hampered scientific inquiry into cannabis and the endocannabinoid system; it’s not yet known what mechanisms may underlie the therapeutic benefits of cannabis for PTSD. Nevertheless, one thing is for sure: this ancient and powerful plant may offer healing to a number of people who otherwise would continue to suffer.

For more information, please see: Walsh, Z., Gonzalez, R., Crosby, K., Thiessen, M. S., Carroll, C., & Bonn-Miller, M. O. (in press). Medical cannabis and mental health: A guided systematic review. Clinical Psychology Review.

Connect with a Cannabis Friendly Clinic and Connect with GrowWise Health

One of the biggest challenges patients continue to face is access.

Because so many physicians remain in the dark about the benefits of medical cannabis, you may be required to ask your physician for a referral to a clinic where you may be assessed by a physician experienced with cannabis therapy. When you and your physician are considering the referral clinic, it is important to remember that assessments services are covered by OHIP and that you should avoid any clinic that charges patients hefty fees to be seen by a doctor.

In an effort to promote greater access for patients, the GrowWise Health team helps patients connect with healthcare providers who can assess their candidacy for medical cannabis. GrowWise Health provides free of charge ACMPR medical cannabis education services to patients for whom medical cannabis may be an appropriate treatment option.

GrowWise Health Patient Educators assist patients in selecting the strain(s) most appropriate for their condition and symptoms and provide guidance on dosing, safety and modes of administration. The GrowWise Health team provides medical cannabis patients with ongoing support to help improve their quality of life.

GrowWise Health Patient Educators provide services for patients in Toronto, Brampton, North York, Niagara Region/Fort Erie and across Ontario and Canada.

If you are interested in learning more about how GrowWise Patient Educators can help you meet your health goals, or to connect with a healthcare provider, please fill out the form below.