A recently published study in the journal Scientific Reports is presenting evidence to suggest molecules called terpenes synergistically interact with cannabinoids to contribute to the therapeutic effects of cannabis. The research supports a controversial hypothesis dubbed the entourage effect, which claims the medical benefits of cannabis are not due to single cannabinoids such as THC or CBD but rather the broader interactions between various compounds in the plant.

The idea behind the entourage effect first arose in the late 1990s after a team of researchers discovered several fatty acids can enhance the activity of endogenous cannabinoids. On their own these compounds do not affect cannabinoid receptors, but when combined with naturally occurring cannabinoids they can amplify receptor activation.“Very seldom is the biological activity of the active constituent assayed together with the inactive ‘entourage’ compounds,” the 1998 research stated. “In view of the results described above investigations of the effect of the active component in the presence of its ‘entourage’ compounds may lead to observations of effects closer to those in Nature than investigations with the active component only.”

This small hypothetical aside slowly grew into the belief that isolating specific chemicals from cannabis for therapeutic uses may not be as effective as administering those same chemicals in their original plant form. The idea of the entourage effect has been especially prominent in the world of cannabis, with advocates of the hypothesis arguing whole-plant extracts are more effective than isolating specific cannabinoids such as THC or CBD.The scientific evidence proving the entourage effect, however, is still lacking. A critical review of research on the subject published last year called most work on the entourage effect “unjustifiably optimistic," and warned the hypothesis is often used to justify “unfounded marketing claims.”

“Claims of a cannabis entourage effect invoke ill-defined and unsubstantiated pharmacological activities which are commonly leveraged toward the popularization and sale of ostensible therapeutic products,” the review stated. “Overestimation of such claims in the scientific and lay literature has fostered their misrepresentation and abuse by a poorly regulated industry.”

There are hundreds of distinct chemical compounds in cannabis. The two well-known compounds are cannabinoids tetrahydrocannabinol (THC) and cannabidiol (CBD). These are the two most active molecules in cannabis, with THC accounting for the plant’s popular psychoactive effects and CBD offering increasengly compelling.Another class of compounds in cannabis are terpenes. More than 100 different terpenes have been catalogued in cannabis and the molecules often are responsible for the distinctive smell of the plant.

Advocates of the entourage effect hypothesis often pint to terpenes as potentially playing a major role in the phenomenon. However a robust study published last year struggled to find any interaction between terpenes in cannabis and cannabinoid receptors. The research also did not detect any synergistic effect of terpenes when combined with THC or CBD.

This new study from researchers at the University of Arizona Health Sciences (UA) offers somewhat differing findings. Using both in vitro cell experiments and in vivo mouse models the researchers investigated the effects of four particular terpenes: alpha-humulene, geraniol, linalool and beta-pinene.

All four terpenes were found to activate CB1R receptors in lab tests. These are the most abundant cannabinoid receptors in the human body.

But why did this study see terpenes activate CB1R receptors when a prior study reached different conclusions? The UA team indicate key differences in their methodology can explain the discordant results.

“[The prior] study used mixtures of terpenes, with no single terpene exceeding 50% of the mixture; they also used a maximum concentration of 10 μM, while we observed receptor activation at higher concentrations,” the researchers note in their new study. “These differences explain our observed results, and in addition, we used an in vivo model, which will capture a broader range of potential activity than an in vitro model with very specific outputs.”The in vivo model in the new study found all four terpenes reduced pain sensation behaviors in the animals. Testing the entourage effect further the researchers used a synthetic cannabinoid called WIN55,212-2 to stimulate cannabinoid receptors.

Pain responses in the animals were reduced more significantly when terpenes were combined with WIN55,212-2, compared to administering either terpenes or WIN55,212-2 alone. The researchers hypothesize this to be an indication of some kind of entourage effect at play.

“It was unexpected, in a way,” says John Streicher, lead researcher on the project. “It was our initial hypothesis, but we didn’t necessarily expect terpenes, these simple compounds that are found in multiple plants, to produce cannabinoid-like effects.”

The researchers are clear in noting these findings must still be confirmed with more relevant cannabinoids such as THC, as opposed to the synthetic cannabinoid used in the study. It is also suggested that further work will need to explore the way this potential synergistic mechanism works as it is still unclear exactly how these terpenes influence CB1R activity. And, on top of all of this, it is still unclear whether the findings of this study point to any meaningful outcome in humans.

The new study is far from definitive evidence proving the entourage effect. The majority of research still struggles to find an entourage effect in cannabis therapeutics. for example, found no difference in effect on cancer cells when comparing pure CBD oil to hemp oils with high CBD concentrations.

Streicher isn’t necessarily an entourage effect evangelist, although he does claim the phenomena is possible  and he is looking closely at whether cannabis terpenes can enhance the pain-relieving effects of other drugs. The goal of his work is to find ways to reduce the side effects of common analgesia by lowering the overall dose of drugs.

“A lot of people are taking Cannabis and cannabinoids for pain,” says Streicher. “We're interested in the concept of the entourage effect, with the idea being that maybe we can boost the modest pain-relieving efficacy of THC and not boost the psychoactive side effects, so you could have a better therapeutic.”