Sleep disturbance is considered by some investigators to be a “hallmark” feature of Posttraumatic Stress Disorder (PTSD) (Germain, 2013). Nightmares and other sleep disturbances are included in the Diagnostic and Statistical Manual of Mental (DSM–5) PTSD diagnostic criteria (APA, 2013). It is estimated that as many as 80-90% of PTSD patients report sleep impairment (Richards et al., 2020). The most common sleep disturbances among PTSD patients are insomnia and nightmares (Krakow et al., 2002, Ohayon and Shapiro, 2000). Research indicates that PTSD patients with higher levels of sleep disturbances have more severe PTSD symptomatology (Short et al., 2014), worse functional disability (Giosan et al., 2015), and a heightened risk of both suicidal ideation (Betts et al., 2013) and self-injury (Short et al., 2015).

It stands to reason, therefore, that treatments that reduce sleep problems, may have beneficial impacts on PTSD. Various medications have been used in attempts to alleviate PTSD sleep disturbances, including nightmares. While some (e.g., Prazosin and Olanzapine) have shown promising effectiveness in sleep disturbances related to PTSD (Lipinska et al., 2016), the management of sleep disturbances in PTSD patients remain challenging, partly due to a lack of standardized delivery and a high dropout rate (van Liempt et al., 2006).

In addition to standard pharmaceutical treatment options, a growing body of research shows that cannabis users, both recreational and medical, including PTSD patients, report that cannabis use improves sleep (Bonn-Miller et al., 2014, Walsh et al., 2013). Research has found that individuals with more severe PTSD are more likely to endorse cannabis to improve their sleep (Bonn-Miller et al., 2014, Metrik et al., 2016). Yet, the evidence base for the effects of cannabis on sleep in general, and in PTSD patients in particular, is limited.

While there are a multitude of cannabinoids and chemical compounds in the cannabis plant, Δ⁹-Tetrahydrocannabinol (THC) and Cannabidiol (CBD) have received the most scientific attention. Within the limited literature on sleep and cannabis, early phase clinical research shows that THC may be effective for improvement in self-reported sleep quality and reduction in nightmare frequency in PTSD patients (Fraser, 2009, Jetly et al., 2015, Roitman et al., 2014). In terms of CBD, research so far has mainly been based on pre-clinical animal models (Elms et al., 2018, Loflin et al., 2017). In one particularly relevant study, CBD administration in a rat model of PTSD showed improvements in sleep (Hsiao et al., 2012). Yet, animal model research has also shown that CBD has alert-promoting effects (Murillo-Rodríguez et al., 2006, Murillo-Rodríguez et al., 2011).

Despite potentially promising results, the preliminary evidence base has some critical limitations. Firstly, the studies examined short-term effects, whereas medical cannabis (MC) for PTSD is typically used for prolonged periods. Research suggests that long-term use of cannabis may lead to tolerance to potential sleep-inducing effects and other PTSD related symptoms (Cuttler et al., 2020, Gorelick et al., 2013, LaFrance et al., 2020, Schierenbeck et al., 2008). Secondly, the experimental studies are limited as they typically test effects of low-dose single (e.g. THC or CBD) molecule extracts or synthetic pharmaceutical cannabinoids administrated sublingually and by standardized dosing. This is very different from real-world everyday use of MC use for PTSD symptoms. Indeed, most MC patients, including PTSD patients, choose to administrate herbal cannabinoids through smoking (Loflin et al., 2019). Herbal cannabis products differ greatly in THC and CBD concentrations and patients tend to use ad libitum dosing regimes and self-titrate to much larger dosages than those typically used in clinical studies (MacCallum & Russo, 2018). Large THC dosages used by healthy individuals have been shown to be detrimental to sleep (Nicholson et al., 2004).

As far as we are aware, only one experimental study has examined the effects of smoked herbal cannabis on PTSD symptoms. The study was a randomized, double-blind, placebo-controlled, crossover trial of ad libitum use of smoked cannabis containing three different concentrations of THC and CBD, and placebo (Bonn-Miller et al., 2021). None of the treatment conditions were associated with reductions in sleep problems. This could be related to the fact that the sample included substantial proportions of participants with previous experience of cannabis use. Thus the results may have been influenced by prior expectations and biased responding. Many participants in this study reported significant cannabis withdrawal symptoms at the time of randomization and early phases of the study. The study illuminates some of the hitherto unresolved challenges related to studying whole plant smoked cannabis in the framework of experimental clinical trials with between-group study designs.