A smokeless method of vaporising and then inhaling dagga packs a much more powerful punch than simply smoking weed, researchers say.
That could raise safety concerns for users – driving, for example.
Marijuana vaporisers heat dagga to a temperature just below combustion, allowing people to inhale the intoxicating chemical tetrahydrocannabinol (THC) from the plant material without breathing in any smoke.
This method produced much more intoxication in a small group of test participants than smoking the same amount of dagga through a typical marijuana pipe, according to the report published online in JAMA Network Open.
More adverse effects
The study participants also had more adverse effects associated with their dagga use when they used vaporisers, and had more pronounced impairment of their ability to think and control their movements, the researchers said.
"It's often a fine line between someone getting the drug effect they desire and having a drug effect that's too strong, and maybe produces paranoia and adverse effects that are uncomfortable for the person," said lead researcher Tory Spindle.
"That sort of thing might be more likely with vaporisers," he added. Spindle is a postdoctoral research fellow at Johns Hopkins University School of Medicine, in Baltimore.
Don't confuse 'vaporisers' and 'vaping'
These vaporisers aren't to be confused with "vaping" – a term used to describe electronic cigarettes.
Survey data has shown that vaporising is becoming a more popular method of using marijuana, particularly in states in the US that have legalised recreational use of the drug, Spindle said.
"It heats it to a temperature that doesn't reach combustion," Spindle said of the vaporising devices. "If you look at the cannabis after it's done vaporising, it doesn't turn into the black ash material it would when you smoke it. It looks exactly like it did when you put it in."
To see if vaporisers deliver a different high than smoking marijuana, Spindle and his colleagues recruited 17 healthy adults who were not frequent marijuana users and asked them to both smoke the drug from a pipe and inhale the fumes produced by a vaporiser.
The same 25mg dose of marijuana produced a significantly stronger high when vaporised than when smoked, the findings showed. Pre-rolled joints sold at dispensaries typically contain 1g of marijuana.
People on vaporised dagga also showed greater impairment than when they smoked the drug, based on testing that gauges the ability to think, reason and perform fine motor skills.
Vaporised dagga came with more side effects as well, including heart racing (24% versus 18% for smoked), paranoia (17% versus 10%), hunger (38% versus 33%), dry mouth (67% versus 43%), and red eyes (25% versus 16%).
Blood tests revealed that people had much higher levels of THC in their circulation after using a vaporiser, about 14.4 nanograms per millilitre (ng/mL) of blood compared with 10.2 ng/mL when they smoked dagga.
The effects typically wore off between six to eight hours for both vaporised and smoked dagga, the researchers said.
More chemicals consumed
Heating but not burning dagga appears to ensure that more of the weed's high-producing chemicals are imbibed by the user, Spindle said.
"Our theory is that when you combust cannabis, more of the THC is lost due to the combustion process," Spindle said. "The vaporiser is a more efficient delivery method than the smoked cannabis."
People who don't use marijuana regularly should approach vaporisers with caution, said Nadia Solowij, a professor at the University of Wollongong in Australia.
"There is a perception that it is a safer route given that it avoids burning the plant matter, thus reducing toxins formed by that process," said Solowij, who wrote an editorial accompanying the new study. "These findings raise concerns for inexperienced users, which include those using [marijuana] both recreationally but also trying cannabis for medical reasons," she added.
"It may be wise to use a smaller amount of cannabis in a vaporiser to achieve the desired effect," Solowij concluded.