policy

State Cannabis Sales Limits Leave Potency Unregulated

As of January 2020, 11 states and the District of Columbia allowed adult use of cannabis and 10 states allowed commercial sales. The majority of these states set sales limits based on the product’s weight, despite significant variation in the amount of tetrahydrocannabinol (THC) in these products.

Now, a new study by researchers from the School of Public Health, University of Southern California, and RAND finds there is considerable variation across states in the total grams of THC allowed to be purchased in a single transaction, but all states allow the equivalent of more than 500 10-milligram doses of THC to be purchased in a single transaction—enough for a typical daily user to be supplied for a month or more.

In the absence of federal regulations, each state that legalizes cannabis must develop its own regulatory system for sales and consumption. The study, published last month in the American Journal of Preventive Medicine, examines the differences in state regulatory environments, including limits on sales.

“These cannabis sales limits are not very useful without limits on the total amount of THC in the transaction or limits on the potency of the products,” says Jason Blanchette, a postdoctoral associate in the Department of Health Law, Policy & Management, and a coauthor of the study.

Sales limits are usually set to encourage moderation and prevent diversion from the legal to the illegal market, says study lead author Rosalie Liccardo Pacula, who is the Elizabeth Garret Chair in Health Policy, Economics & Law at the University of Southern California Schaeffer Center and professor of health policy and management at the USC Price School of Public Policy. “The limits applied by U.S. states today will not accomplish either of these objectives,” Pacula says.

“Sales limits are an underused intervention in public health but there’s an opportunity to get this right to reduce youth use and adult excessive use of cannabis and hopefully to use as an example for limits on other consumer products like tobacco, firearms, and alcohol.”

“Policy makers should adopt limits on the potency of cannabis products for other reasons too because, for example, a lot of consumers are getting surprised by the extremely high potency of their products and unintentional overconsuming.”  

The researchers found that states that allow legal retail sale of recreational cannabis established sales limits, typically based on the weight of each of the cannabis product sold. For example, limits on the sale of flower and/or bud are set at 1 ounce for all but two states—Maine and Michigan—which set their limit at 2.5 ounces. Concentrates similarly have weight-based limits imposed, ranging from a low of 3.5 grams in Nevada to a high of 15 grams in Michigan.

On face value, these seem like small deviations from relatively innocuous amounts of each product. The problem, the researchers say, is that the weight of a product tells nothing about the amount of THC, the main psychoactive ingredient in cannabis used to measure potency. The amount of THC in each class of products can vary substantially. Flowers and bud material can vary from 8 percent to 34 percent THC, while concentrates can vary from 40 to 97 percent THC, based on real products sold on the market in Washington State.

Therefore, the total grams of THC purchased in a single transaction can vary significantly even when the same quantities of cannabis are being purchased.

“A person purchasing the maximum amount of flower and concentrate in, say, Nevada could walk away having purchased 3.67 grams of THC if they stuck to the lowest potency products, or 13.03 grams of THC if they purchased the highest potency products,” says Timothy Naimi, lead scientist on the grant, which was provided by the National Institute on Alcohol Abuse and Alcoholism.

“It would be far more transparent if all sales limits were based on the amount of THC, rather than the weight of the product.” Naimi is now the director of the Canadian Institute for Substance Use Research at the University of Victoria, Canada, but he conducted this research when he was a physician and faculty member at SPH and Boston Medical Center. 

The researchers found that if all products sold had minimum product potencies, the grams of THC sold in a transaction could range from 2.3 grams in Massachusetts to 10.5 grams in Michigan. At maximum product potencies, grams of THC per transaction range from 5.6 in Alaska to 33.6 in Michigan.

Unlike alcohol or tobacco, there is no set dose or serving for cannabis, but the industry and scientists are converging on standardized doses of about 5 to 10 milligrams of THC.

Assuming a 10-milligram dose, all states allowed for single purchases exceeding 500 THC-standardized doses assuming average potency of the product. Six states allowed single purchases exceeding 1,000 doses and one state allowed more than 2,000 doses to be sold in a single transaction.

Given that the typical daily user consumes approximately 320 milligrams of THC in a day, these quantity limits suggest that they can purchase enough cannabis in a single transaction to last two weeks in any state. They can easily purchase even more than a two-week supply if they only purchased high-potency products.

As an increasing number of states consider legalizing cannabis, these findings show why caps on total transaction amounts and dosing measurements are important, the researchers say. They argue that if regulators intend to encourage moderate consumption of THC, then limits should be based on the quantity of THC—otherwise, individuals interested in purchasing a large amount of THC can simply purchase products with increased potency.

Such limits can also prevent unintentional overconsuming, as many consumers are surprised by the high potency of the cannabis products they purchase, Blanchette says.

“Sales limits are an underused intervention in public health but there’s an opportunity to get this right to reduce youth use and adult excessive use of cannabis, and hopefully use as an example for limits on other consumer products like tobacco, firearms, and alcohol,” he says.

This study was also coauthored by Marlene C. Lira of Boston Medical Center and Rosanna Smart of the RAND Corporation.