, new data from a small study suggested.
Participants who inhaled vaporized D-limonene and THC reported significantly greater decreases in anxiogenic effects than did people who received either component alone or a placebo. Reductions were greater as the dose of the D-limonene was increased.
Investigators noted that the findings could have implications for the use of medicinal or recreational cannabis, which has increased in recent years due to state legalization efforts.
“People use cannabis to help reduce anxiety, depression, and posttraumatic stress disorder, but since THC levels vary widely, if a person overshoots their tolerance of THC, cannabis can induce anxiety rather than relieve it,” senior investigator Ryan Vandrey, PhD, professor of psychiatry and behavioral sciences, Johns Hopkins School of Medicine, Baltimore, said in a news release.
“Our study demonstrates that D-limonene can modulate the effects of THC in a meaningful way and make THC more tolerable to people using it for both therapeutic and non-therapeutic purposes,” he added.
The study was published online in Drug and Alcohol Dependence.
Entourage Theory
Cannabis legalization has opened the door to an increased range of medicinal and nonmedicinal uses, but its benefits can be limited by the anxiety and panic some people experience with its use, investigators noted.
Many cannabis plants have been bred to contain higher concentrations of THC, with some dispensaries selling cannabis with more than 20%-30% THC. The plants often include cannabidiol, “minor” cannabinoids, and terpenes, such as D-limonene.
Prior studies pointed to THC as the cause of acute behavioral and psychoactive effects some cannabis users experience. However, a new, untested theory, the “cannabis entourage effect theory,” suggested other components in cannabis, including D-limonene, may contribute to the anxiogenic symptoms.
“We were motivated by scientific publications that hypothesized D-limonene can attenuate the acute anxiogenic effects of cannabis, but for which empirical data did not exist,” Dr. Vandrey said.
Investigators designed a small double-blind, within-subjects crossover study of 20 healthy adults (median age, 26 years; 50% men). About half of participants were Caucasian/non-Hispanic, 30% African American/non-Hispanic, 10% Caucasian/Hispanic, and 10% Asian/non-Hispanic.
All participants completed nine outpatient drug administration sessions, during which they inhaled vaporized D-limonene alone (1 or 5 mg), THC alone (15 or 30 mg), the same doses of THC and D-limonene together, or placebo.
Primary outcomes included subjective drug effects, measured with the Drug Effect Questionnaire (DEQ) and the 20-item state subscale of the State-Trait Anxiety Inventory (STAI-S). Investigators also measured cognitive/psychomotor performance with the Digit Symbol Substitution Task (DSST) and the Paced Serial Addition Task.
Vital signs such as heart rate, systolic blood pressure (SBP), diastolic blood pressure (DBP), and plasma D-limonene and THC concentrations were also tracked.
Participants’ responses were measured at baseline and then an additional nine times after initial exposure over the course of each 6-hour test session. Blood and urine samples were collected from participants before, during, and after each session.
First Evidence
There were no significant differences in outcomes between the D-limonene alone and placebo groups.
Receipt of 15- and 30-mg doses of THC alone was associated with subjective reports of acute cannabis exposure, including cognitive and physiological effects.
A treatment effect was observed for “anxious/nervous” (P < .01), “paranoid” (P < .01), and “heart racing” (P < .0001).
In planned comparisons, ratings of anxiety-like subjective effects qualitatively decreased as D-limonene dose increased, and concurrent administration of 30-mg THC plus 15-mg D-limonene significantly reduced ratings of “anxious/nervous” and “paranoid” on the DEQ compared to 30 mg of THC alone (P < .05).
Findings were similar on the composite score of the STAI-S, and although planned comparisons did not reach the threshold for statistical significance, reductions in anxiety approached significance in the THC plus D-limonene group compared with the THC alone condition (P = .08). The combination group also reported significantly lower subjective ratings of unpleasant drug effects than the THC alone group (P = .03).
In particular, a main effect of treatment was found for the anxious/nervous category on the DEQ (P < .01), as well as the “paranoid” (P < .01) and heart racing (P < .0001) categories.
On the other hand, ratings of anxious/nervous and paranoid categories were significantly lower in the 30-mg THC plus 15-mg D-limonene vs the 30-mg THC alone condition (P < .05, for all).
As for cognition, following drug administration, a significant main effect of treatment was observed for the DSST (P < .05), but no significant differences between THC and THC plus D-limonene combination conditions or between D-limonene alone and placebo were detected.
There were no differences within each THC dose and between D-limonene alone versus placebo conditions. Moreover, there were no main effects of treatment found for SBP or DBP.
The combination condition produced significantly greater concentrations of THC than the THC alone condition (P < .05).
“This study provides the first evidence that there are chemical constituents found naturally in the cannabis plant that can reduce some of the adverse effects of using delta-9-THC,” Dr. Vandrey said.
Although the exact mechanism by which vaporized D-limonene counters the anxiogenic effects of THC is unclear, “our best guess is that D-limonene is producing an anxiolytic effect on its own that is not mediated by cannabinoid receptors,” Dr. Vandrey said.
Significant Impact
Commenting on the research, Joshua Lile, PhD, professor, Department of Behavioral Science, University of Kentucky College of Medicine, Lexington, noted that the study seems to be the first of its kind to study the influence of terpene on THC response.
The research “makes a significant impact on our field,” and is “among the few controlled clinical studies that have demonstrated interactions between THC and other cannabis constituents, supporting the validity of the ‘entourage’ effect,” said Dr. Lile, who was not involved with the current research.
“This work is particularly important, given the unfounded claims sometimes made by the cannabis industry regarding the effects of different cannabis products,” he added.
Also commenting on the study, Ziva Cooper, PhD, professor and director of the UCLA Center for Cannabis and Cannabinoids, University of California Los Angeles, said the findings “have direct implications for improving the safety of cannabis, whether it’s being used for medical or nonmedical purposes, especially in people and patients who do not have experience with cannabis, a group that is at high risk for experiencing anxiety after using cannabis.”
In addition, “an important aspect to this study is that the effects of limonene in reducing anxiety attributed to delta-9-THC were observed at higher concentrations (or doses) than those usually present in the plant,” Dr. Copper said. “This calls for further investigation into new cannabis formulations specifically designed to leverage the potential protective effects of the terpene.”
This research was supported by the National Institute on Drug Abuse. Dr. Vandrey served as a consultant or received honoraria from Mira1a Therapeutics, Inc.; Jazz Pharmaceuticals; Charlotte’s Web; Syqe Medical Ltd.; and WebMD. The other authors’ disclosures are listed on the original paper. Dr. Lile declared no relevant financial relationships. Dr. Cooper reported receiving study drug from Canopy Growth Corp and True Terpenes, study-related materials from Storz & Bickel, and research support from the National Institute on Drug Abuse, National Center for Complementary and Integrative Health, California Department of Cannabis Control, Center for Medicinal Cannabis Research, and California Highway Patrol.
A version of this article appeared on Medscape.com.