“I don't think anyone conceptualized what would happen when ... industry and science and business and the motivation of profit come into the state of Washington,” said Washington state Rep. Lauren Davis, a Democrat, who has twice introduced legislation to cap THC potency in concentrates, products such as oils, wax and shatter. “All of a sudden, a few years later, your shelves are stocked with these oils that are 99 percent THC.”

The cannabis industry — with $20 billion in legal sales last year — is pushing back hard against proposals like Davis’. And so far, they’ve successfully squelched legislative efforts in statehouses across the country, including Florida, Washington and elsewhere. Only Vermont has THC potency caps in place, with flower products limited to 30 percent and concentrates capped at 60 percent.

“We welcome the conversation about public safety, and want to be an active part of it. But a potency limit is a nonstarter,” said Truman Bradley, executive director of Colorado’s Marijuana Industry Group, arguing that regulatory restrictions are a better way to ensure product safety. “It’s not effective as a public health tool.”

But the issue isn’t going away. Proposals to limit the potency of THC have been introduced by both Democrats and Republicans, and are likely to proliferate as the legal pot market expands and matures. Lawmakers in Congress have also expressed concern about the increasing potency of weed. Last month, the co-chairs of the Senate Caucus on International Narcotics Control — Dianne Feinstein (D-Calif.) and John Cornyn (R-Texas) — argued that federal agencies should consider recommending THC caps.

Supporters of THC caps argue that they’ll protect unwitting consumers from ingesting highly potent products without significantly infringing on the rights of marijuana enthusiasts. There’s also a deeper concern that kids and young adults will have access to ever more potent products. Brain development typically continues until the age of 25, and chronic marijuana use has been shown to impact that process.

“There's a lot of statutory tightening that we need to do to help rein in what is clearly a problem, which is diversion of high-potency products into the hands of teenagers,” Colorado House Speaker Alec Garnett, a Democrat, said in an interview. “I don't want a teenager to be confronted with a question of whether or not to dab a high-potency concentrate.”

Increasingly, parents are raising alarm bells about the issue. In Colorado, for example, Blue Rising Together, a Democratic-aligned group founded to advocate for gun control legislation, has expanded its agenda to push for THC potency caps.

Davis said she’s given up on working with the cannabis industry on this issue after a 2020 congressional work session where state industry lobbyists repeatedly claimed that cannabis was not a cause of psychosis.

“They were sitting there, doing exactly what Philip Morris did, exactly what Purdue Pharma did — trying to poke holes in science and question that consensus of the scientific community,” she said.

The industry’s argument

Data is dodgy and incomplete about exactly how strong weed has become. The average potency of marijuana products seized by the DEA in 2019 topped 14 percent — more than triple the average potency of products seized in 1995, when the National Institute on Drug Abuse first began collecting data.

But that doesn’t reflect the reality of marijuana products broadly on the market. In states where recreational sales are legal, flower regularly tops 20 percent and marijuana concentrates often have potency levels of 60 to 80 percent, or even higher.

Industry advocates dismiss the push for THC potency caps as the latest version of reefer madness. They argue that dodgy science and irrational fears are driving the debate, and that marijuana should be treated the same as alcohol, with state regulators empowered to ensure that products are safe. They also stress that putting arbitrary limits on the potency of products will simply drive consumers accustomed to those products — whether for medical or recreational purposes — into the illicit market.

Morgan Fox, spokesperson for the National Cannabis Industry Association, points to the 2019 vaping crisis as a warning sign of what could go wrong. More than 2,800 individuals were hospitalized and 68 people died from mysterious lung illnesses that were largely tied to illegal THC vaping products.

“High potency products like concentrates — there's significant demand for them among cannabis consumers,” Fox said. “If you make it so that regulated producers are no longer able to produce these, that market is going to go completely underground.”

Kevin Sabet, president of the anti-legalization group Smart Approaches to Marijuana, argues that illegal drug dealers don’t have the manufacturing expertise and infrastructure to produce the types of high-potency products that have flourished in state-legal markets.

“The reason we even have high potency products is because of the legal market,” Sabet said. “They invented this. Pablo Escobar did not invent this. Mexican drug cartels never came up with this stuff. This is American ingenuity, and it's American ingenuity gone wrong.”

Kris Krane, the president of marijuana company 4Front Ventures, disputes this assertion. He points out that concentrated THC products have long existed on the illicit market, albeit not in the variety that is found in legal markets today.

“It doesn't take that much to do butane extraction in a garage,” Krane said. “It's just really dangerous.”

Imperfect science

Garnett, the Colorado speaker, argues that the disconnect between state and federal laws has made it more difficult to gather credible scientific data about the impact of high-THC products. That’s hamstrung lawmakers looking to address the issue without unnecessarily stifling the industry.

“The biggest drawback to the feds not participating in this conversation earlier is the fact that they haven't activated the FDA and the NIH to do the public health research on the developing and mature brain and what happens when high potency products are used,” Garnett said. “If we could rewind, that is the one place that I wish the federal government would have taken a leading role.”

Most scientists agree that the research isn’t complete. But they also argue that each new study makes a more compelling argument for limiting the availability of high-THC products. The human brain’s formation is assisted by the body’s endocannabinoid system, explained Deepak Cyril D’Souza, a Yale University scientist who has studied the relationship between cannabis and psychosis for 25 years. It’s a system that includes receptors and chemical messengers that play an important role in brain function through age 25.

“What happens is the endocannabinoid system — when it turns on — its effects last for just a few milliseconds to seconds. But when someone smokes cannabis, that system is turned on not for seconds to milliseconds, but for minutes to hours,” D’Souza said. “And so exposure to cannabis during these critical phases of brain development can be messed up, for lack of a better word.”

Davis’ Washington state bill differs from other THC potency cap proposals, because it would limit the purchase of concentrates to individuals over the age of 25. Flower, edibles and other cannabis products with lower THC levels would still be available to anyone over the age of 21.

Legislative dead ends

So far, efforts to impose potency caps have largely sputtered out in state capitals.

Nowhere has the issue gotten more attention than in Florida, where the debate has played out for three straight years. The state’s booming medical marijuana program has more than 530,000 participants, adding more than 200,000 enrollees in just the last year.