As Vermont rolls out its regulated cannabis market, discussions about its implementation continue to address tetrahydrocannabinol, or THC, caps. Written into statute, these caps determine what products Vermonters will find on dispensary shelves, how potent they will be and what impact they could have on consumers' health.

THC caps may also affect the profitability of Vermont's cannabis producers and retailers, as well as their ability to compete with those in neighboring states. They might even influence the drug tolerance levels of habitual users.

What are THC caps, and why does Vermont have them? Simply put, they're the upper limits of how strong cannabis can be in all of its forms.

Act 164, which created Vermont's recreational market, designated which products are legal to sell based on their concentration of THC. Often described as the chief intoxicant of cannabis, THC is actually one of dozens of cannabinoids and terpenes that combine to create a high. Nevertheless, THC is what's used to measure and regulate cannabis potency; the more THC, the stronger the dose.

By law, it will be illegal for adult-use dispensaries to sell cannabis flower — the dense, pungent buds that are smoked or vaped — with THC levels above 30 percent. Also prohibited is the sale of solid concentrates, such as edibles, hashish and dabs, with THC levels above 60 percent. However, liquid concentrates, of the prepackaged variety used in battery-operated vape pens, have no such limits.

Proponents of lower THC caps include the Vermont Medical Society, the American Academy of Pediatrics Vermont Chapter and the Vermont Psychiatric Association. Testifying on behalf of all three groups, Jill Sudhoff-Guerin — the policy and communications consultant with the VMS — told the House Committee on Government Operations in February that cannabis products with concentrations above 15 percent have been linked in other states to rising emergency room visits for mental health disorders, respiratory distress and cannabis hyperemesis syndrome, or uncontrolled vomiting.

Sudhoff-Guerin also cited studies linking high-potency pot to cannabis use disorder, especially among teens and young adults. Currently, Vermont has one of the highest rates of young adult cannabis use in the country.

But opponents of THC caps say that such limits don't achieve their intended goals and will only harm a budding industry that will compete against neighboring states, such as Massachusetts, with no caps. Many opponents support either eliminating the caps entirely or letting Vermont's Cannabis Control Board set them.

Geoffrey Pizzutillo is cofounder and executive director of the Vermont Growers Association, a nonprofit trade group representing more than 70 cultivators, processors and distributors. Pizzutillo said that THC caps on flower are absurd because "nature is not a machine," and THC levels can vary from branch to branch within a single plant.

Pizzutillo also noted that, in other states, solid concentrates comprise 50 percent of the retail market. Banning half the products of the kind sold in Massachusetts will only drive Vermont's small, artisanal producers into the unregulated market and push consumers across state lines.

"We understand that sometimes [THC caps are] politically palatable," said DeVaughn Ward, senior legislative counsel for the national Marijuana Policy Project, which also opposes THC caps. "But from a policy standpoint, they're not very helpful."

Consider edibles, Ward said. If THC is capped at 5 milligrams per edible rather than 10, a consumer who wants a 10-milligram dose will simply eat two edibles, much the way a drinker will consume a second beer or cocktail if one doesn't provide the desired buzz.

Ward's argument raises an interesting question: Is there a difference between someone consuming a high-potency cannabis strain versus consuming more of a lower-potency strain? And is cannabis comparable to alcohol, in that someone can have two drinks of a 40-proof liquor or one drink of an 80-proof liquor and get equally intoxicated?

There are no simple answers, according to Tom Fontana, a licensed clinical mental health counselor, alcohol and drug counselor and part-time cannabis researcher at the University of Vermont. When it comes to dosages, Fontana explained via email, consuming two edibles with 10 milligrams of THC is basically equivalent to eating one 20-milligram dose. (Smoking flower changes the equation somewhat, he noted, due to THC lost in burning and "sidestream" smoke, but that's another story.)

But as for achieving a comparable high by halving the potency but doubling the dose, Fontana said, "the science is not clear." What's more, alcohol is not a useful analogy.

Alcohol, he explained, is dose dependent: The more alcohol in your system, the drunker you are, with peak intoxication coinciding with peak blood alcohol content.

With cannabis, peak impairment doesn't necessarily correspond to peak THC levels in the body. Fontana pointed to research showing that you can spike THC levels in the body without causing a comparable uptick in intoxication. Or, as he put it, "There seems to be only so high someone can get."

Fontana predicts that, initially, market forces will drive potency levels upward. For the first few years of legal retail sales, he wrote, many consumers will try to get more "bang for their buck" and, all else being equal, will buy the higher-THC product if it's available.

Lethal overdoses aren't a concern with cannabis. As the National Cancer Institute website explains, cannabinoid receptors in the brain aren't located in areas that control breathing, unlike those for opioids. And while some people talk about cannabis dependency, its addictive potential is "considerably lower" than other drugs such as opioids and cocaine, the NCI notes.

That said, high-potency cannabis can still pose dangers to users, Fontana said. It can make it harder for them to "self-titrate," or control how high they get. Another risk is "greening out," or having adverse effects such as nausea, dizziness, disorientation and anxiety.

Finally, he said, higher-potency pot also increases habitual users' THC tolerance, requiring them to seek ever-higher dosages.

For now, the legislature appears unlikely to alter the current THC caps before the retail market opens on October 1 or earlier. In December, the Cannabis Control Board recommended that the legislature remove the 60 percent cap on solid concentrates and allow the board to regulate those products instead. But even with current caps, cannabis is far more potent today than it was 20 years ago due to improved cultivation techniques and greater consumer demand.

So, expect to hear a refrain common in other adult-use markets: This is not your parents' pot.

Correction, April 21, 2022: The story was updated to include the Cannabis Control Board's recommendation that lawmakers remove the 60 percent cap on solid concentrates and allow the board to regulate those products instead.