Penn prof. determines amount of marijuana in an average joint

For years, experts have debated the amount of marijuana contained in the average joint, and a new study by criminology professor Greg Ridgeway and Beau Kilmer of the Rand Corporation offers an answer: about one-third of a gram, lower than some previous estimates.

Understanding the amount of weed consumed in a typical joint is important for discussions surrounding the drug in both political and healthcare contexts. Marijuana is often sold by the joint in both legal and illegal markets. If someone wants to know how much weed people are smoking, for issues such as tax projections or public health studies, you need to know how much weed is in an average joint.

“If you are trying to estimate total marijuana expenditures, make realistic projections about tax revenues, or understand how a policy change will influence the illicit market, you need to have good information about consumption," Kilmer said 

The study, published in the journal Drug and Alcohol Dependence, looks at 10 years of arrest data to estimate average joint size. Using a drug pricing model and statistical analysis, the two researchers came up with a mean weight of 0.32 grams of marijuana per joint.

Previous studies have offered a range of estimates when it comes to joint size. A 2011 study of 251 participants yielded an average of 0.66 grams per joint. More recently, a 2014 federal report estimated the figure to be about 0.43 grams.

Because users often report marijuana consumption in terms of joints smoked, self-reported consumption data is not very useful without an accurate estimate of joint size.“In order to get good projections, you need to be able to turn those answers — ‘I’ve had one joint in the last 30 days’ — into a quantity,” Ridgeway told The New York Times.

A number of factors can complicate estimates, particularly when self reporting is involved.

“Much depends on the type of user being surveyed, where they live, how the question is worded, and whether there were visual prompts,” Kilmer said.

Admittedly, Ridgeway and Kilmer only addressed a subpopulation of 10,000 marijuana users in U.S. cities during a federal program from 2000 to 2010. Prices paid and amounts purchased were based on participants’ reports.

The challenge in measuring consumption does not end at estimating joint size. The popularity of other methods of consumption, such as concentrates and edibles, presents complications for researchers.

“While joint size info can help inform these estimates, we also need data about the consumption of other cannabis products,” Kilmer said.

Changes in drug potency also pose challenges. Over the 10-year period analyzed, the average amount of THC in a joint likely increased, the study noted.

Still, Ridgeway and Kilmer’s study is one of the more robust in recent years. The joint size estimate is also notably lower than previously reported figures.

“These estimates can be incorporated into drug policy discussions to produce better understanding about illicit marijuana markets, the size of potential legalized marijuana markets, and health and behavior outcomes,” the two researchers wrote.

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