While no one is exactly sure how strong cannabis was in the 1970s, one thing most people agree on is that levels of tetrahydrocannabinol (THC), the main psychoactive compound in cannabis, have increased dramatically—or even exponentially—since that time. As high-potency cannabis flower has given way to even more potent cannabinoid concentrates and extracts, discussion has turned to the possibility of limiting THC content in cannabis products to protect consumers from high doses of the ingredient.
The good news about THC is that in adult users, it’s rarely associated with adverse medical effects. This is the reason for the distinction many cannabis users and industry insiders make between the term “overdose” (applicable to potentially fatal or physically health-risking drugs like opioids or cocaine) and the recent term “green-out” (meaning an excess dose of THC leading to acute discomfort and disorientation). The bad news is that a large dose of THC has the potential to leave users suffering through hours of confusion and terror, even while presenting little physical threat.
With those concerns in mind, many states have started to crack down on the potency of infused cannabis foods by imposing “potency caps,” which refer only to the potency of THC (rather than cannabidiol [CBD], for example), since that cannabinoid is responsible for psychoactive effects and, likewise, is responsible for the discomfort associated with an uncomfortably large dose.
THC Potency Limits
Colorado was the first U.S. state to experience national pushback for its “wild west” climate of unregulated products and, accordingly, the state was early to adopt regulations to control edibles. In 2017, Colorado banned edibles that could be confused with candy and limited edible products to a maximum 800 mg of THC per package.
As of 2021, many other states have implemented THC caps on edibles that are between 50 mg and 100 mg per package; at the same time, Colorado has dialed down its maximum limit into that range. However, other states, such as Illinois and Montana, have per-package limits as high as 500 mg and 800 mg, respectively. Most states mandate a maximum serving of 5 mg to 10 mg but allow many servings per package. (A chocolate bar containing 100 mg will be broken down into 10 squares, each containing 10 mg of THC.) The most extreme approach comes from Canada, where federal regulator Health Canada has capped edibles potency nationally at 10 mg of THC per package.
Who Is at Risk from Edibles?
The urge to protect children comes from legitimate concerns, says Daniele Piomelli, PhD, the Louise Turner Arnold Chair in the Neurosciences and Director of the Center for the Study of Cannabis at University of California, Irvine. “Doing no harm is the first thing one must always think about: The Hippocratic oath of ‘Do No Harm’ is also a good strategy in life,” he says. “To do no harm with THC, the first thing one must do is identify vulnerable populations: groups of folks who are at risk of developing toxicity if they’re exposed to high doses of THC.”
One group we know can be adversely affected by high doses of THC is teenagers still undergoing brain development in regions of the cortex full of cannabinoid receptors. A second group, pregnant women, may also be adversely affected by THC. Among teenagers, the research is fairly stark. “We have substantial data from animal work, but also epidemiological data from human populations, giving the sense that [teenagers are] a population that should be warned against excessive use of THC,” Dr. Piomelli concludes. “[Teenagers] should not see high levels of THC, ever, or if they do, they should take that only very occasionally.”
Outside of teenagers and pregnant women, Dr. Piomelli is less concerned about high doses of THC, noting, “When it comes to adults, the risks of THC, even at high doses, are relatively minor. They can be offset by some education: the idea that you want to avoid frequent use to prevent developing a habit or use disorder. If you use frequently, keep your doses low. There are ways we can reduce harm, because luckily THC is not a very toxic substance to adults.”
For these reasons, Dr. Piomelli opposes THC caps as an unwise approach. “Caps on potency, just like caps on prices, end up being circumvented by the black market—and we have a gigantic black market, especially in states like California where regulations are very tight. Once something goes into the black market, as the word indicates, it’s a black hole: We have no data, and we lose control of the safety issues.”
The Government’s Challenge
Katharine Neill Harris, PhD, the Alfred C. Glassell Fellow in Drug Policy at Rice University’s Baker Institute for Public Policy in Houston, agrees, though she also understands Dr. Piomelli’s concern about potential risks to younger users. “I get the urge to limit the amount of THC,” she says, “Some of the efforts to limit THC content come from very good intentions and public health concerns. But I don’t really think it can have the intended effect at this point. The time to have tried to limit the amount of THC in any of these products was 30 years ago, long before the illicit market started getting saturated with high-potency products. The cat’s out of the bag on that. We’re not going back. Because the government didn’t regulate this decades ago, it missed that opportunity, and the illicit market adapted to create high-potency products.”
This circumstance presents leaders with the difficulty of balancing public health concerns against the profit motive of what is clearly a booming business, Dr. Harris says. “Once you create an industry that has a profit incentive, and people are using these products and using them more regularly,” she says, “you’re sort of automatically sacrificing something to public health with the creation of that market. That’s how we’ve done it, and there could have been a conversation about government regulation of these things—for example, only having the government supplying edibles, and they could make it so there are no edibles available for purchase above a certain amount.”
Would cannabis users trust government guidance? Dr. Harris isn’t sure, saying that she thinks the average marijuana consumer is unlikely to trust what the U.S. government is saying about cannabis. In practice, she says, this will make it difficult for federal government agencies above all to try to educate consumers about safer cannabis consumption. One outcome of this distrust, she suggests, is that consumers may not believe warnings about the acute discomfort of excess THC unless they’ve experienced it themselves.
A second concern Dr. Harris raises about caps on THC is that nearly every cap—either suggested or enshrined in law—is arbitrary. While we know high-potency THC can be connected with adverse effects and bad experiences, we have no hard numbers to indicate which doses connect with which harms. “We don’t have research saying, ‘above 15%, that’s when it becomes [risky].’ The limits that are being proposed by state legislators are just arbitrary numbers,” she says. “I don’t know where any of them come from. I haven’t spoken with the legislators behind the bills. I don’t know where the people proposing these bills are getting the ideas for these limits. I haven’t seen anything in the literature that provides definitive guidance.”
Accordingly, legislators tend to choose numbers divisible by five as their cap targets. “These are nice easy numbers, and the products that have been on the market have been divisible into amounts like that—that’s what people have experiences with,” Dr. Harris says. “But we don’t have any research that tells us what people feel like when they take 5 mg or 10 mg. We don’t have that research because it’s a Schedule 1 drug and we have no facilitated research to look more at the effects of cannabis use beyond concluding that it’s bad for us.”
Achieving the Same Goals without THC Limits
All of these commentators agree that the rise of highly potent edibles presents public health concerns, chiefly related to the possibility that such high doses may be consumed by minors with still-developing brains. Likewise, all of them oppose THC caps in favor of other means of discouraging high THC consumption.
For Dr. Piomelli, the best means of limiting THC consumption is through economic incentive. “I’m very much in favor of increasing the price and putting a price on high-level THC,” he says, noting that such an increase shouldn’t be steep, but just enough to sway potential users away from the stronger products, and ideally encourage buyers to consume lower-THC products in general. “The price premium they pay should be enough to dissuade them from using it very frequently. I see price escalation—as a function of amount of THC in a given preparation—as a reasonable compromise. That would be consistent with the complexity of the pharmacology of THC.”
Dr. Harris agrees, though she urges care in setting taxes that raise prices on cannabis, since this could drive consumers back to illicit sellers. She believes a modest tax applied, based on THC content, might do the trick, though she also counsels measures that encourage the consumption of CBD as a means of reducing potential mental health harms. “Don’t just punish high-THC, but encourage the use of products that have CBD or that are less potent in THC,” she says. “One of the concerns people have about high-THC products is about psychosis and [adverse mental health effects]. Research shows CBD can counteract some of the psychoactive effects of THC. To breed high-THC flower, they remove all the CBD, but you can put it back in with concentrates. We have edible products with 25 mg CBD and 10 mg THC.”
If the federal government were to get into the game, Dr. Harris says, telling consumers to mediate their THC consumption with CBD, that might be useful, provided consumers believe government sources.
Public education is the core of concern for Jay D. Wexler, a professor at Boston University School of Law. He supports measures that focus on informing consumers, such as the widespread packaging requirements now in place across most, if not all, U.S. states where cannabis is legal, which demand labeling that clearly states how much THC an entire package of edible products contains. Along with this information, Dr. Wexler calls for education programs to more effectively introduce the edibles mantra of “start low and go slow” to the widest possible American public.
“When we sell liquor, you buy it in the whole bottle,” he says, “you don’t buy little shots of it. My whiskey comes in [units of] 20 shots. We teach people how the stuff affects them, what’s in the bottle, and it’s not so hard.”
THC Potency Limits May Discourage Moderation
But even alcohol is a strange comparison for Dr. Piomelli, who comes from Italy and reports a dramatically different culture of moderate alcohol consumption in that country. “In the U.S.—or other countries—we’ve never been politically willing to explain to people what is a healthy culture of alcohol,” he says. “We tend to fall back on the prohibitionist idea that no quantity of alcohol is good for you, and you’re better off not ever using it. This is the position of the American Medical Association, and it’s so extreme that it ends up undercutting the credibility of the statement. It belies the personal experience of millions of people across entire countries.”
With that attitude in mind, Dr. Piomelli says a cap on THC is the wrong way to get consumers to use cannabis in moderation. “Having the government impose a cap hasn’t worked in the past.”