US health officials have urged people to stop using the devices for now.
In Massachusetts, the state agency also does not regulate vaping cartridge hardware, even as lab tests and media reports suggest the heating coils in some cheap Chinese-made pods could leach heavy metals into the vapor they create.
Experts warned the lack of oversight around vape additives leaves consumers at risk, and the state flying blind into an emerging public health crisis.
“It’s not enough to say, ‘We know what the active ingredient is, so it’s fine,’ ” said Dr. Sharon Levy, director of Boston Children’s Hospital’s substance use program, adding that popular vape cartridges bear little chemical resemblance to the marijuana plant, which has a long history of human consumption. “Actually, very small differences matter. We’re ignoring all of that. That is a very basic problem.”
So far, none of the patients whose cases are under investigation are from Massachusetts, but state officials said they are investigating “several” possible cases. One patient who died had used a marijuana vape from a licensed store in Oregon.
Cannabis commissioner Jen Flanagan said the agency should discuss whether to regulate additives.
“Everyone should be on alert when they’re vaping anything,” she said.
Vaporizers typically heat concentrated marijuana oil with battery-activated coils. Experts say the resulting vapor can harm the lungs.
The US Centers for Disease Control and Prevention has identified an oily vitamin E-derived compound as a possible common link among some cases, The Washington Post reported. However, federal officials stressed they have yet to make a definitive determination, and continue to analyze samples for a broad range of chemicals, including “cutting agents.”
The state cannabis commission is investigating whether products sold at licensed marijuana stores in Massachusetts include the vitamin E-related compound, a spokeswoman said.
Several Massachusetts marijuana executives said they are unaware of any licensed companies that use the compound, but that it is sometimes used by unregulated manufacturers to lighten their extracts’ color.
While questionable additives are more common in illicit marijuana cartridges, they are also present on the shelves of state-regulated marijuana shops.
“There are no rules about what can and can’t go in a vape pen,” said Chris Hudalla, a chemist who runs Milford-based marijuana testing company ProVerde Laboratories. “It’s absolutely problematic.”
New England Treatment Access, which runs a cannabis store in Brookline, sells inexpensive vape pens cut with propylene glycol, a common food additive that experts said could be dangerous to inhale. And Alternative Therapies Group, which runs a pot store in Salem, uses a similar chemical, polyethylene glycol, in some of its vapes. A study published this week in the Journal of Clinical Investigation found that inhaling the vapor of propylene glycol harmed the lungs of mice.
NETA said propylene glycol is safe, and no customers have reported negative health effects. Still, the company is developing other inexpensive vape cartridges that are free of the substance.
“I’m a chemist and I wouldn’t want to vape propylene glycol,” said Michael Kahn, the president of MCR Labs in Framingham, adding that the drug has only been shown to be safe for oral consumption.
While Chris Edwards, the chief executive of ATG, said he believes polyethylene glycol is safe, his company — like many others — is phasing it out in favor of terpenes, a class of aromatic chemicals found in cannabis and other plants.
While tiny amounts of terpenes are naturally present in marijuana and give different strains their scents, marijuana companies sometimes add significant quantities of both cannabis-derived and other terpenes to state-approved vape pods to improve flavor and viscosity.
That practice concerns even some marijuana company owners.
“Terpenes are pretty caustic,” said Brandon Pollock, chief executive of Theory Wellness, a marijuana retailer. “Take limolene — we use that to clean stainless steel tables. To put something like that in a vape that you’re going to heat up and inhale seems risky.’’
Recently, Pollock said, customers have been asking Theory Wellness about the safety of its vape cartridges. The firm’s vapes contain only cannabis and small quantities of cannabis-derived terpenes, he said, adding that the state should consider making that the rule.
“The whole point of legalization is to protect public health and make sure people are getting a product that’s tested and safe,” he said.
Marijuana consumers were surprised to learn that Massachusetts imposes no limits on vape additives.
“It’s messed up — who knows how they’re deriving it?” said Steven Cerrato, 27, a musician from Dedham who has regularly visited NETA. “Twenty, thirty years might go by and everyone might have a weird cancer.”
State rules require that marijuana products be tested for pesticides, heavy metals, potency, mold and other microbes, and residual solvent chemicals used in processing. Manufacturers also must list ingredients on product labels. However, the commission doesn’t verify whether the listed ingredients are accurate, or that additives are safe to heat and inhale.
Hudalla, the chemist, said he is also concerned about the cartridge hardware, nearly all of which is made in China. Using a “smoking machine” that puffs on vaporizers, his lab has found metals such as aluminum and chromium in the vapor from unregulated cartridges that were not present in the concentrate itself, suggesting the contamination came from the device’s heating coils.
While the commission doesn’t require regulated manufacturers to test their cartridges, some operators including Garden Remedies and NETA said they do so voluntarily.
Public health experts said regulated cartridges, which are tested and labeled, are far safer than those purchased on the street, but they said it’s a dangerous oversight to allow the pot industry to add any chemicals it chooses to vape cartridges.
At the same time, they conceded that state regulators face a difficult challenge: There is little data on the safety of marijuana vaporizers because the drug is still illegal under federal law.
Dr. Michael Siegel, a public health professor at Boston University, said state marijuana officials should probably regulate additives, but that consumers should not panic.
“These products have been on the market for awhile and we haven’t seen a problem with them,” he said.