As political and legal space open for cannabis in state after state, the idea of caps on potency — whether of flower, extracts or edibles — is gaining currency among legislators. But voices in the cannabis industry view this as a phobic response rooted in the deeply flawed assumptions of prohibition.

What does the science actually have to say on this question? Are legal maximums for tetrahydrocannabinol (THC) content sound policy, or an updated version of “reefer madness”?

Potency cap defeated in Florida – for now

A proposed measure in Florida to cap the potency of medical marijuana failed to become law this year — much to the relief of the Sunshine State’s cannabis community.

House Bill 1455, which was advancing through the Republican-led state Legislature this spring, would have limited the amount of THC in smokable cannabis to just 10% by volume. That’s considerably less than what most dispensaries offer to the state’s 533,000 registered medical marijuana users. Edibles would have been limited to 15%, and extracts to 60%. Terminal patients would have been exempt from the limits — which implies that products exceeding the caps would still have been available on a highly restricted basis.

But the Health Committee met for the last time this session on April 19 without hearing the bill, meaning it did not go to a floor vote.

“I think the bill is effectively dead,” the sponsor, Rep. Spencer Roach (R-Fort Myers), conceded to the Miami Herald. “Anything is possible … But right now I don’t see a path forward.”

And indeed, the legislative session ended April 30, which means the bill will have to be introduced anew in the next session.

Health concerns or ‘reefer madness’?

In the political fight over the measure, Roach repeatedly invoked the state’s deadly opioid abuse problem. For instance, he told Tallahassee’s WFSU in March: “[J]ust like the opioid crisis, we saw it overprescribed and we saw this medication getting trafficked across state lines. We saw it ended up in our high schools and being sold to children.”

The Democratic opponents of the measure, and the cannabis industry, dismissed such concerns as “reefer madness.” They emphasized that a deadly overdose on cannabis is impossible — in vivid contrast to opioids.

Agriculture Commissioner Nikki Fried — Florida’s only statewide elected Democrat and herself a medical marijuana user — was among those celebrating the demise of the measure. “Thank God for all of the activists that came up to Tallahassee, that signed the petitions. That’s what democracy looks like: When we get together, we hear from the people, and legislation that would have hurt them is stopped,” Fried told the Miami Herald.

There are fears of a replay in the next legislative session. In 2020, the Florida House voted to pass THC caps for medical marijuana patients younger than 21, in a measure attached to a larger healthcare bill. However, the cap was stripped out of the final version that unanimously passed that March.

Roach and Sen. Ray Rodrigues (also a Republican from Fort Myers), who sponsored the cap measure in the Senate this year, said they are undecided on whether to re-introduce the measures next session.

“I think the industry has done a very good job of spinning this narrative that ‘Spencer Roach is trying to take away your medicine,’” Roach conceded to the Herald. “I think we lost the battle for the narrative on this one.”

THC limits in other states

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Proposals to limit THC levels, however, seem to be gaining momentum nationwide. Even in Colorado and Washington, the states that pioneered adult-use legalization with their successful ballot initiatives in 2012, legislators are debating whether to instate caps on cannabis potency. And the rhetoric is akin to that heard in Florida. Nor is it only coming from Republicans.

In Washington, state Rep. Lauren Davis, a Snohomish County Democrat, has twice introduced measures to cap potency in concentrates sold to those under the age of 25. “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,” she told Politico. “All of a sudden, a few years later, your shelves are stocked with these oils that are 99% THC.”

In Colorado, Blue Rising Together, a Democratic-aligned organization launched to advocate for gun control legislation, is now also petitioning for cannabis potency caps.

Vermont last October actually enacted potency caps in S.54, the act establishing a regulated adult-use market in the Green Mountain State. Under the law, flower is capped at 30% THC, while concentrates are capped at 60%. Edibles have a 50-miligram limit per package, and 5-miligram cap per serving. These limits do not apply to medical marijuana or home-cultivated cannabis; nor to non-ingestible infused products, such as topicals. Gov. Phil Scott, a Republican, did not sign S.54, but declined to veto it — thereby allowing it to become law without his signature.

And Virginia’s new legalization law, signed in April by Democratic Gov. Ralph Northam, gives the yet-to-be-seated Cannabis Control Authority the power to establish THC limits.

Taxing by potency

Then there is the idea of taxing by potency, which is also gaining currency. New York’s new legalization law, signed at the end of March by Democratic Gov. Andrew Cuomo, instated taxation on the basis of THC content, on top of a flat sales tax. This potency tax imposes 0.5 cents ($0.005) per one milligram of THC in herbaceous flower, 0.8 cents ($0.008) per milligram in concentrates, and three cents ($0.03) per milligram in edibles.

The legalization law in Illinois, signed by Democratic Gov. JB Pritzker in 2019, also instates a potency-based tax structure. It imposes a 25% tax rate for products with THC concentration above 35%, compared to 10% for products that fall below that threshold.

The California Legislative Analyst’s Office also recommended a potency tax in 2019, stating that such a policy “could reduce harmful use more effectively.”

And even on Capitol Hill, where bills to legalize cannabis nationwide are currently pending, the idea of potency caps is under consideration. The Senate’s bipartisan Caucus on International Narcotics Control — headed by Dianne Feinstein (D-Calif.) and John Cornyn (R-Tex.) — suggested in March that federal agencies should consider recommending THC limits.

Split in the medical establishment?

As Tallahassee’s WSFU pointed out in its coverage of the Florida fight, physicians are among those pushing back against the potency crackdown. In a Zoom call as the bill was advancing in the Legislature, a group of Florida doctors who certify patients for medical marijuana cards challenged Roach’s assertions.

Former emergency room physician Barry Gordon, who now owns the Compassionate Cannabis Clinic in Venice, said during the call:  “We’re not a pill mill, we’re not an accessory to anybody’s drug crisis. Patients are coming to me with three desires every single day — they want to feel the best they can; they want to do it in the safest, most natural, most plant-based, least pharma [way]; and most controllable … way that they can.”

But most media coverage portrayed a split in the scientific establishment about the risks of cannabis use in youth and young adults — meaning those 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,” Yale School of Medicine researcher Deepak Cyril D’Souza told Politico. “And so exposure to cannabis during these critical phases of brain development can be messed up, for lack of a better word.”

The reports also emphasized that THC levels in cannabis flower have been increasing over the past decades — supposedly, from 4% in 1995 to 12% in 2014 in pot seized by federal agents. “This is not your Woodstock weed,” Kevin Sabet, president of Smart Approaches to Marijuana, the anti-legalization group that seems to be agitating for potency caps as a rearguard strategy, told the Associated Press. “We need to put some limitations on the products being sold.”

The AP also cited a 2017 study, “The Health Effects of Cannabis and Cannabinoids,” by the National Academies of Sciences, which listed increasing potency among factors that “create the potential for an increased risk of adverse health effects.”

AP balanced these fearful voices with quotes such as that from Cristina Buccola, a cannabis business lawyer in New York, who said: “It’s prohibitionism 2.0. Once they start putting caps on that, what don’t they put caps on?”

Potency & Psychosis

However, much is left out of this presentation of the competing views. Whatever the unproven risks of cannabis use to the developing brain may be, does it necessarily follow that higher potency means a greater likelihood of harm?

As some cannabis advocates have argued before, there is a case to be made that high-potency strains are actually beneficial, as they require users to smoke less to achieve the same effect — sparing the lungs exposure to tar and carcinogens. The assumption that users of such strains are all getting significantly higher than did their parents or grandparents during the Woodstock generation is questionable.

Yet this assumption appears to lie behind much of what is being misrepresented as objective science. The Denver Post on April 28 wrote: “Growing evidence shows high-potency THC products are more likely to bring on or worsen mental health issues in young people.” It backed up this claim by citing a July 2020 report from the Colorado Public Health Department, “THC Concentration in Colorado Marijuana Health Effects and Public Health Concerns,” which stated: “We found SUBSTANTIAL evidence that THC intoxication can cause acute psychotic symptoms, which are worse with higher doses.”

Also cited was a January 2021 study in the Journal of the American Medical Association, which (in the Post’s paraphrase) “found elevated risk of self-harm among young people who misused cannabis.”

But this may all be based on erroneous assumptions. After an outburst of media hype about a possible psychosis link to high-potency “skunk” strains a few years ago, critics even within the scientific community pointed out that studies finding such a link could be confusing mere correlation with causality. Those struggling with psychotic symptoms or an urge to self-harm may be (consciously or not) self-medicating with cannabis. So words like “misuse” may be essentially reading things backwards.

Racism & the politics of potency

The bizarre case in France of the admitted assailant in a clear-cut anti-Semitic murder avoiding criminal charges on the basis of “cannabis-induced psychosis” does indeed point to re-emergent reefer madness. But the cannabis stigma is more often used to convict than acquit, at least in the court of public opinion — and especially on the U.S. side of the Atlantic.

In the famous case of George Floyd, which sparked the Black Lives Matter uprising last May, it was his supposed use of methamphetamine that was invoked by Minneapolis authorities in what Floyd’s family dismissed as a “red herring.” More often, cannabis has been the substance at issue in the posthumous stigmatization of the victims of racially biased police killings.

Some of the most notorious cases of recent years:

  • In July 2016, Philando Castile was killed by a cop during a traffic stop in the Twin Cities area. The cop won his acquittal partly on the basis of the allegation that Castile had been high on cannabis at the time of the shooting. No cannabis was found in the vehicle, but it was touted that a blood test posthumously performed on Castile came back positive for THC.
  • In July 2015, Sandra Bland was found hanged to death in her Texas jail-cell after a traffic stop. Authorities made much of the fact that her autopsy showed she’d been using cannabis. Her death was ruled a suicide — to the outrage of her family.
  • In August 2014, Michael Brown was killed by police in Ferguson, Mo., sparking the first national Black Lives Matter demonstrations. A copy of Brown’s autopsy was leaked to the St. Louis Post Dispatch, which ran the following headline: “Official autopsy shows Michael Brown had close-range wound to his hand, marijuana in system.” This was again assailed as an effort to stigmatize the victim.
  • And in February 2012, 17-year-old Trayvon Martin was killed by vigilante George Zimmerman while walking home from buying Skittles in Sanford, Fla. Zimmerman was notoriously acquitted on the bizarrely implausible basis of self-defense. His defense team attempted to introduce as evidence that the youth’s autopsy had shown trace amounts of THC in his bloodstream. The lawyers won approval from the judge to admit this as evidence, and the lead attorney actually told the media that even a small level of THC in the bloodstream could increase violent behavior. The toxicology report indicating cannabis use was ultimately not submitted to jurors, probably because the lawyers judged that it wouldn’t fly — a small victory for common sense, at least.

So there are weightier political implications to the potency question than either side in the debate may acknowledge. Especially when the dubious notion of cannabis-induced psychosis is invoked, the potency scare does seem all too redolent of 1930s “reefer madness,” in which the marijuana menace was blatantly linked to the racist fears and fantasies of white America.

Stigma versus science?

Project CBD turned to Nashville-based neurobiologist Greg Gerdeman, PhD, for some clarity on the potency question.

“The focus on percentage of the composition is misguided,” Gerdeman tells Project CBD. “It comes from arbitrary origins, like deciding that hemp is cannabis with 0.3% THC or less. Potent cannabis and preparations of cannabis have been around for a very long time, and highly potent THC products have been approved as medicine, especially Dronabinol.” That’s the legally available anti-nausea medication marketed in the US as Marinol — which is about 90% THC. It comes in doses of up to 10 milligrams THC per pill.

Percentage of THC does not necessarily correlate with how powerfully one could be intoxicated if one consumes a given product. “It can be used safely,” Gerdeman explains. “If you’re concerned about over-consuming, what’s at issue is how many milligrams of THC — not the percentage of them.”

“With a more concentrated product, it’s reasonable to think you can get to that higher level more quickly,” Gerdeman concedes. “It’s not that I think percent values are meaningless. But one can consume a small amount of a high-percent THC product and still consume a low number of milligrams functionally. People have been able to successfully titrate their consumption that way for as long as people have been consuming hash oils and other extracted products. And these things are not as new as the opponents like to present.”

“Potent hash and hash oil have been around,” he elaborates. “Various cannabis-based medicines that were widely available before prohibition included tinctures and infusions and syrups that were distilled or reduced extracts of cannabis. And they were even at times favored for their potency by doctors — for ease of reaching a therapeutic dose and, I suspect, greater reliability.”

Gerdeman points to a book in his personal collection, a hefty volume entitled The United States Dispensatory, 22nd and Centennial Edition by Wood & LaWall, published by Lippincott in 1937 — the same year the federal government effectively outlawed cannabis. Surprisingly, it makes note of commercial imports of cannabis to the United States from India, for medicinal use, stating: “Cannabis is used in medicine to relieve pain, to encourage sleep, and to soothe restlessness … [I]n some persons it appears to produce a euphoria and will often relieve migraine headaches.”

It’s paragraph on the potency question is revealing: “One of the great hindrances to the wider use of this drug is the great variability in the potency of different samples of cannabis which renders it impossible to approximate the proper dose of any individual sample except by clinical trial. Because of occasional unpleasant symptoms from unusually potent preparations, physicians have generally been overcautious in the quantities administered. The only way of determining the dose of an individual preparation is to give it in ascending quantities until some effect is produced. The fluid extract is perhaps as useful a preparation as any; one may start with two or three minims of this three times a day, increasing one minim every dose until some effect is produced.” (A minim is one sixtieth of a fluid dram, or one drop of liquid.)

“In other words, start low and go slow,” Gerdeman interprets. “It’s basically describing the state of knowledge we have 80 years later — start low and tritate up. Having consistency in the potency of the medicine is more important than setting arbitrary caps.”

Standards & transparency versus rigid maximums

The focus on percentages becomes especially problematic where edibles are concerned, in Gerdeman’s view. “There can be 33 milligrams of hemp-derived THC in a single cookie, but the cookie itself weighs several grams — that is, several thousands of milligrams — so it is still within 0.3% limit. Now, that’s where people can start having adverse reactions. Even with a cap of 0.3% you can consume large amounts of THC in edibles.”

Asked for his view of the best safeguard against this, Gerdeman replies: “I think there should be truth in advertising. It’s important to have standards and transparency. If you’re selling a product that can get you really high, it ought to be known as such.”

He sees an obstacle to this in the “cat-and-mouse gamesmanship that the history — and ongoing story — of prohibition has engendered.”

“There are patients that require high doses for the therapeutic effect they need, and also people with high tolerance to THC,” Gerdeman adds. “I think people should be cautious using high concentrations of THC, but I also think there are valid medical uses for high-concentrate THC products. And some people use these high-concentrate products recreationally and do so safely. There should be accurate labeling, and responsible vendors should educate consumers about the effects of high-THC concentrates. Just like liquor should be consumed responsibly. But I don’t think prohibition is the answer. I don’t think it should be prohibited by law. I do think it should be regulated.”

Asked about taxation by potency, Gerdeman is quick to emphasize: “I don’t think it should be taxed at all if it’s for a legitimate medical need.”

Above all, he refutes the notion that a causal link between potency and deleterious effects is established, objective science. “I’ve looked at the literature very carefully for over 20 years,” Gerdeman says. “I believe where research has shown cognitive impairment, it is in individuals who started using cannabis very heavily, very frequently, from a very young age. It is not tightly tied to potency. That is conjecture on the part of the scientists.”

He concludes: “Obviously, high-THC products shouldn’t be legally sold to kids — and they aren’t. But, as we’ve seen with liquor, you can only do so much in terms of policy.”


Bill Weinberg, a Project CBD contributing writer, is a 30-year veteran journalist in the fields of drug policy, ecology and indigenous peoples. He is a former news editor at High Times magazine, and he produces the websites CounterVortex.org and Global Ganja Report.

Copyright, Project CBD. May not be reprinted without permission.