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As Canada Legalizes Weed, Switzerland Wants to Get High on Moss

Mice injected with a THC-like compound found in liverworts acted as if they were stoned—lazing around more, not moving for long periods of time, and feeling less pain.
liverwort and cannabis nugget
The forest plant liverwort (left) won’t get you as high as cannabis (right). Liverwort image: University of Bern/Stefan Fischer. Cannabis image: Shutterstock

While Canadians cash in on their ability to buy legal cannabis, other parts of the world are finding other plants that offer similar health benefits.

Liverworts might sound like something out of a Harry Potter book but these moss-like plants are a legal high for recreational and medicinal users in Switzerland, New Zealand, and possibly other parts of the world. The plants contain perrottetinene (PET), a compound chemically similar to tetrahydrocannabinol (THC), the psychoactive chemical in weed.


Anecdotally, liverworts send users on a mild trip, similar to smoking weed, where they feel “tingly” or “out of body.”

Now, biochemistry researchers in Switzerland have confirmed that the liverwort compound works in the body in a similar way to THC and it might even be better than weed for medicinal use.

In a study published Wednesday in the journal Science Advances, researchers pitted PET against THC in a battery of tests to determine which chemical receptors it activates and how mice behave under the influence.

Read More: Still More Evidence That All Weed Is the Same

Although you can buy liverwort pretty easily online, its concentrations of PET are variable and overall quite weak. The scientists would have had to have bought vast quantities to get enough of the compound to work with. Instead, they synthesized both THC and PET with help from the Eidgenössische Technische Hochschule in Zürich.

To figure out how the compound acts on a chemical level in the body, the research team combined PET or THC with hamster ovary cells that make the 44 most common receptors (the proteins on the outside of a cell that receive chemical signals) andenzymes found in mammal bodies, proteins, and neutral buffer solution.

“We had to start completely from scratch,” said lead researcher and biochemist Jürg Gertsch. “We didn’t want to get bias, so we thought, ‘Ok let’s do a total profile of the compound and which receptors in the brain it interacts [with],’” he told me over the phone.


The team found that PET works in a similar way to THC but with a few key differences. Like THC, PET bound to the cannabinoid receptors CB1 and CB2 but at levels around 10 times lower. It also bound to the mood receptors serotonin and dopamine but only at much higher concentrations.

What this means, according to Gertsch, is that liverwort probably doesn’t give you the same euphoric high as cannabis, because it doesn’t activate the receptors as strongly and doesn’t trigger cells to make fat-like molecules associated with that high.

Unlike THC, PET was found to reduce levels of anti-inflammatory molecules swishing around in the solution, which would likely result in fewer side effects and make it act as a pain reliever.

“In a direct comparison I think perrottetinene is the better version of THC,” Gertsch concluded.

Despite any chemical difference, mice injected with PET acted like they were stoned—lazing around more, not moving for long periods of time, and feeling less pain.

Gertsch thinks liverwort’s chemical characteristics make it a prime candidate for medicinal use in reducing pain and inflammation. New Zealand’s indigenous Māori people have used it as a traditional medicine for centuries to treat digestive or liver problems. Without the strong psychoactive effects, liverwort might be more appealing to pharmacologists and lawmakers than cannabis.

“There is this stigma [around] THC and also the individual reaction of people [differs]. The dosing is sometimes difficult and people are afraid of overdose,” he said.


Currently Switzerland, where Gertsch is based, allows growing and selling cannabis strains that have less than 1 percent THC and instead contain the non-psychoactive compound cannabidiol (CBD). Only one cannabis product is sold legally for medicinal purposes but terminally ill patients can request the drug.

Getting to the stage where concentrations of liverwort are sold in pharmacies is a long road, Gertsch explained. They would first need to test the compound on mice models of pain or inflammation, find a way to make the molecule (maybe by putting the genes that code for PET into another moss), figure out the right dosing, screen for any side effects, and eventually conduct human trials. That process, he said, requires a “huge investment.”

Timothy Welty, a pharmacy professor who helped develop an epilepsy drug from CBD and who was not involved in the study, says the research is interesting but agrees it’s still in the very preliminary stages.

Before researchers can even consider animal or human trials, they would need to know more “basic background,” he told me over the phone. That is, knowing more about how PET interacts with receptors in a living organism, rather than in a petri dish, and experimenting with modifying the chemical structure of the molecule to make it more effective. Then comes the drug development (do you put it in a tablet or inject it?) and figuring out how it would be absorbed, used, and eventually eliminated by the body.

The entire process could take ten years, Welty said.

When I asked Gertsch if it wouldn’t just be easier to legalize cannabis he replied with a chuckle, “Sure, that’s an ongoing discussion here as well. It’s very bureaucratic.”

According to reports, the black market for cannabis with higher levels of THC, or products that provide a similar effect, are flourishing in Switzerland. Discussions around legalizing cannabis for medicinal purposes are currently underway, with changes to the law potentially coming into effect by summer 2019.

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