At least two Minnesotans using legal medical cannabis have suffered vaping-related lung injuries, but health officials aren't blaming legal pot or limiting access to state-sanctioned products because those users also vaped illicit products containing THC.

While all vaping-related lung injuries are checked to see if the patients are on the state's medical cannabis registry, most cases involved patients who used illicit forms of THC, the psychoactive component in marijuana, said Dr. Ruth Lynfield, epidemiologist for the Minnesota Department of Health.

"We want to keep our eyes open, but thus far it really does seem as though the illegal THC products are what is driving the injuries, at least in Minnesota," Lynfield said in an interview.

Minnesota has reported 72 probable or confirmed cases, and one death, related to the national outbreak of vaping-related lung injuries this year. Another 31 potential cases are under review, including two additional patients on the state's cannabis registry.

Nationally, there have been at least 1,299 cases of vaping-related lung injuries and 26 deaths, according to the U.S. Centers for Disease Control and Prevention. While some patients vaped nicotine alone, the majority used THC. On Friday, CDC officials urged people not to vape THC — and didn't differentiate between legal or illicit forms — until the causes of the outbreak are identified.

State health officials sent an alert last month to the 18,000 people certified to receive medical cannabis in Minnesota, noting that illicit THC was behind most injuries but that they "cannot give complete assurance of the safety of any specific vaping product until investigators determine a cause." However, they said Monday that they have no plans to halt distribution of inhaled forms of legal cannabis.

Roughly 60% of cannabis products sold by the state's two approved distributors are vaped forms. Other forms include pills, liquids and creams.

One of the distributors, Minnesota Medical Solutions, said in an e-mailed statement that enrollment and purchase of vaping products has remained stable, though more patients are asking pharmacists about alternatives.

The other, LeafLine Labs, announced this month that it was conducting additional safety testing of vaping products, but offered patients the opportunity to exchange products purchased within 30 days.

Switching isn't simple for some patients, who might prefer vaping because it provides the fastest pain relief or because they have trouble swallowing pills, said Chris Tholkes, interim director of the state Health Department's office of medical cannabis.

"We encourage patients to have the discussion with their health care providers and with the pharmacists at the cannabis patient centers that they are using … to figure out what is best for them," she said.

Minnesota first legalized medical cannabis in 2015, and now permits it for people with any of 14 qualifying medical conditions approved by the state, including cancer and intractable pain. State officials are considering whether to add macular degeneration and chronic pain to the list.

Nationally, the CDC has tallied self-reported information from 573 patients and found that 76% used products containing THC, often in combination with e-cigarettes containing nicotine. The federal agency didn't break out the data by legal or illicit forms of THC.

Illicit THC products might contain chemicals or additives such as vitamin E that may be contributing to the lung injuries. The U.S. Food and Drug Administration has received hundreds of product samples from lung-injured patients, but hasn't found a common cause.

Minnesota hasn't sent samples to the FDA but has conducted its own testing, Lynfield said. Results have been inconclusive, but she said she suspects the outbreak will be traced to a change or additive to illicit products this year, because there were so few lung injuries in prior years.

Among 53 lung-injury cases reviewed by Minnesota health officials, 23 involved patients who needed treatment in intensive care, often with mechanical ventilation to maintain their breathing. Many involved otherwise healthy teenagers.

"Something different was going on this year," Lynfield said. "I don't think we would have missed a bunch of young adults being in the intensive care unit" in prior years.

Jeremy Olson • 612-673-7744