The main psychoactive component of cannabis appears to reduce persistent and distressing nightmares in people with post-traumatic stress disorder (PTSD). Dronabinol—a purified form of tetrahydrocannabinol (THC) extracted from cannabis plants—was more than twice as likely to lead to complete cessation of nightmares in people with this mental health condition compared with placebo. Although it is unclear why it produces this effect, THC may suppress the sleep stage in which dreams are most likely to occur.
Around 4 per cent of the world's population suffers from PTSD at some point in their lives. The condition causes people to repeatedly relive a traumatic event, frequently through nightmares. Treatments such as trauma therapy can help, but they are not always readily accessible, and no intervention specifically targets relieving nightmares.
Stefan Röpke, from Charité–Universitätsmedizin Berlin hospital in Germany, sees people with PTSD daily and says that some report getting relief from their nightmares if they take a small amount of cannabis before bed. "That was the reason for the trial," he said.
Röpke and his colleagues recruited 171 people with PTSD who experienced frequent and intense nightmares, assessed using a standard 0 to 8-point scale. Eighty-seven of the participants were instructed to take dronabinol—approved for treating nausea and vomiting caused by cancer medications, and loss of appetite in people with acquired immunodeficiency syndrome (AIDS)—one hour before bed each night for 10 weeks. The remaining 84 participants took a placebo. They started with 2.5 milligrams and gradually increased the dose until their nightmares stopped or they reached the maximum dose of 15 milligrams.
Röpke emphasises that people should not self-medicate with cannabis: "Treatment with dronabinol and other similar interventions should be prescribed and monitored by a doctor".
After 10 weeks, the severity of nightmares decreased by around 3.7 points in the dronabinol group—1.5 points more than the placebo group. "An improvement of 4 points could mean having nightmares several times a week with considerable distress at the start and having only occasional and slightly distressing nightmares after treatment," Röpke said.
"Based on the moderate effect size for the nightmare outcome, I would say the findings are clinically relevant," said Carrie Cuttler from Washington State University.
The researchers also found that 58 per cent of the dronabinol group experienced at least a 50 per cent reduction in the frequency and intensity of their nightmares, compared with 29 per cent of the placebo group. Additionally, 37 per cent of the former group experienced complete cessation of their nightmares, compared with 15 per cent of the placebo group. "What impressed us most was the magnitude of the effect," Röpke said.
The psychoactive effects of THC meant that approximately 4 out of 5 participants who took it calculated that they were not in the placebo group. However, half of those who received placebo thought they had received dronabinol. Expectation of an effect may explain some of the results, but probably not all, Röpke said.
One theory is that THC alters signalling in the brain's endocannabinoid system. This helps regulate processes including sleep and how brain cells communicate, which could lead to fewer nightmares. It may also suppress the rapid eye movement (REM) stage of sleep, when the most vivid dreams occur, although studies on this have produced mixed results.
"If they are not dreaming as much, then they will not have nightmares," Cuttler said. "The problem is that if they stop using THC, there is REM rebound, and they have really severe nightmares".
The researchers observed a small increase in sleep disturbances during the two-week follow-up period after the study ended. Cuttler says this could encourage nightly use of dronabinol, which does not address the root of someone's PTSD. "Symptoms return once they recover from intoxication and that leads them to need to use more of the drug, and that can create a cannabis use disorder or dependence".
Seven people who received dronabinol experienced a serious adverse event, which the researchers say was not caused by the treatment, compared with none in the placebo group.