Colorado examine sheds new gentle on marijuana efficiency, intoxication


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Measuring cannabis poisoning has been an unsolvable equation despite the spread of legalization. Blood tests and roadside breathalyzers can detect THC in our bodies, but tolerance and consumption time have a dramatic effect on how severely we are really affected. Regular users can still have high levels of THC in their blood after not consuming a pot for more than a day, while inexperienced users can be significantly impaired hours after smoking, even though their blood is not high enough to be considered legally impaired to become.

University of Colorado Boulder Professor Cinnamon Bidwell and her team of researchers tried to crack this code by using a mobile laboratory to examine 121 regular users before, during, and after smoking cannabis flowers or concentrates by performing tests to have performed memory, balance and cognition. Results, released in June, showed that while cannabis users were affected for up to an hour after consumption, the effectiveness of products – from 16 percent THC for flowers to 90 percent for concentrates – did not correlate with participant scores.

We recently spoke with Bidwell about the variables of cannabis poisoning and how accurate the current roadside THC tests really are.

Westword: How important is THC tolerance when trying to find out the effect of cannabis potency on poisoning?

Cinnamon Bidwell: Tolerance certainly plays a role here, but the question also arises whether the THC levels in the blood are that high. This was likely related to effectiveness, and the concentrate users had higher levels of THC exposure for the most part. It’s hard to imagine simply building a tolerance to this level of THC. Hence, for people who are interested in, or even tolerate, these types of products, there may be something different biologically.

How quickly do users develop a tolerance for THC? Did you notice that the tolerances among the participants increased during the study?

The main question of the study was: Does the level of impairment track the effectiveness of the products? To answer this tolerance question, you need to track people over long periods of time and while taking certain types of products. These are exactly the questions we would like to pursue this study with. Has anything changed for concentrate users after a tolerance break or a period of no use, less use, or use of a less effective product? Has anything changed in your response to cannabis? Were there any withdrawal symptoms or anything else that we would be concerned about from a health hazard point of view?

Have the concentrated users been regular users from the start? Have you ever seen flower users react to concentrates, or vice versa?

Because of the way cannabis research is done these days, we need to assign products to which they have already been exposed in order to test products that will be used in the real world. Concentrate users must have been exposed to concentrates, as well as flower users who could not be assigned to concentrates during the study.

One of the big things that stood out from a cognitive point of view was that even after the highly potent products, there aren’t many indicators of post-use impairment. Indicators showed that were particularly reminiscent of learned verbal memories, such as instructions they heard, but other forms of perception such as attention or even other forms of memory that did not contain verbal information were not affected after use. We also noted a specific change in equilibrium function that was acutely impaired after cannabis use. However, for both those indicating impairment measures, the results were the same regardless of the use of 15 percent flower, 24 percent flower, or 70 to 90 percent THC concentrates. These domains were affected, but there was no major impairment from higher potency.

Cinnamon Bidwell (left) led a novel study on THC poisoning for the University of Colorado Boulder

Cinnamon Bidwell (left) led a novel study on THC poisoning for the University of Colorado Boulder

Courtesy University of Colorado Boulder

What do you think this study says about Colorado’s current driving limit of 5 nanograms of THC per milliliter of blood?

I think we have to go above the blood level. Our data really supports that. The 5 nanogram limit for roadside testing is problematic because, as you can see from our data, some of our regular users exceeded this value prior to use on a given day. It’s not the best marker, whereas the change in balance we noticed was something that, although subtle, was noticeable after use. Something with a psychomotor or behavioral marker is a stronger indicator of actual recent usage and appears to be much more useful and accurate for public safety.

Did you learn anything during the study about how we recover from THC impairment?

With our verbal memory recall data, we had two points in time after use: immediately after use and one hour after use – and this aspect did not recover over the one hour period. But the markers for balance, or how easily you can stand without swaying, were worse immediately after use and improved an hour later. Is this actually connected worse or less safely with the driver? We didn’t look at this in our study, but these are indicators that show someone has recently consumed cannabis more accurately than their blood.

Are there such conflicts with alcohol testers? Do blood alcohol levels on a breathalyzer necessarily mean the same level of poisoning for everyone?

Recognizing alcohol is a little cleaner. We have a really good grasp of the distribution of alcohol particles in the breath and how they cleanly match blood alcohol levels, and there is strong data showing how those numbers are related to behavioral problems. We don’t have many of these steps with cannabis, like the distribution of THC on oxygen in the breath or how blood levels of THC are actually related to behavioral disorders. We know so much less about cannabis.

What questions would you like to answer after opening this door?

The issues of tolerance are something we’re very interested in, as well as the long-term effects of using higher potency products. When people are exposed to and adapt to this high level of THC over time, or their bodies fail to handle it, are there any long-term consequences? We are interested in looking long-term and what happens to highly effective users when they take a break. We hope to expand our knowledge to include driving and public safety, and to have a reliable, ethical marker that can identify cannabis-related driving disorders.

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Thomas Mitchell has been writing about everything cannabis-related for Westword since 2014, covering sports, real estate, and general news en route to publications like the Republic of Arizona, Inman, and Fox Sports. He is currently the cannabis editor for

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