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The Changing Chemical Composition Of A Burning Cannabis Joint

7 min read

Jan 19, 2024


How does smoking a cannabis joint change the chemical composition of the cannabis joint? 


The therapeutic properties of medical cannabis are attributed to its active pharmaceutical ingredients known as APIs, which are primarily cannabinoids. With well over 100 identified, including well-known compounds like tetrahydrocannabinol (THC), cannabidiol (CBD), and cannabigerol (CBG), cannabis presents a diverse array of therapeutic compounds. Additionally, the plant contains over 200 terpenes, with around 20 being the most prevalent, and then a whole suite of flavonoids, esters and others, including sulfur-containing compounds contributing to the chemical makeup.


A recent study by Eyal et al. called Inconsistency in the Composition of the Smoke of a Cannabis Cigarette as Smoking Progresses: Results, Mechanism, and Implications, has tried to break down what happens to the chemicals in a burning joint. This would explain why the start and end of a joint are different; it explores the role heat plays and might even suggest that smoke itself affects the composition of the unsmoked part of the joint. 


Previously On Puff The Magic Dragon 

Previous investigations into cannabis smoking have mainly concentrated on the hazards of smoking, revealing low delivery yields of cannabinoids in the smoke. However, this study from 2005  shows cannabis cigarettes (joints) are significantly less cancerogenic than tobacco cigarettes. Other studies have shown that up to 50% of cannabinoids can be lost in side-stream smoke, up to 30% destroyed by pyrolysis, and 10% trapped in the butt. Furthermore, smoking parameters such as puff frequency, duration, and volume significantly influence cannabinoid yield. Mixing cannabis with tobacco, a common practice, has been found to increase THC yields, potentially due to differences in combustion temperatures and vapor pressure equilibrium. However, this needs to be investigated further as the adverse effects of tobacco far outweigh the potential increase in THC yield.

  

Combustion Studies Severely Lacking

Despite the critical role of various APIs in the nature and efficacy of cannabis medical treatment, limited research has focused on the smoking delivery yield and rate of provision of APIs beyond THC. In fact, many regions do not allow medicinal cannabis to be smoked, and in the UK, for example, if you smoke your prescription cannabis flower, you are no longer consuming cannabis ‘legally’. Furthermore, many plant treatments, such as pesticide sprays, which are approved for use on food crops, are also allowed by default to be used on cannabis plants with no data whatsoever on the combustion/breakdown of these compounds – a worrying reality of the medical and commercial cannabis world.


Existing studies have reported total terpene content in smoke and concentration of specific terpenes, but comprehensive insights into the composition of inhaled fractions during cannabis smoking remain elusive. Building on recent findings demonstrating significant differences in the evaporation rates of different cannabis APIs when inhaled through a vaporizer, this study aims to contribute to the understanding of multi-API component compositions inhaled during cannabis smoking. Specifically, the research focuses on the reproducibility of smoking results between portions and the mechanistic explanation of these outcomes. Through these investigations, the study shed light on the nuances of cannabis smoking and its impact on the delivery of therapeutic compounds. The control for this experiment was a cannabis flower which had its THC removed through solvent extraction.





Seeing Through The Smoke

While smoking is a standard method of cannabis consumption, there is limited understanding of the yield and provision rate of cannabis APIs during this process. To address this, the researchers conducted ten experiments using a designated smoking machine to study changes in API content during smoking. The evaluation included analysing residuals from the smoked joint and assessing the composition of the smoke, specifically looking at cannabinoid and terpene content. Initially, the focus was on how decarboxylation, a process crucial for activating THC, varies across different parts of the joint. It was found that the part nearest the lit end of the smoked cigarette underwent the most decarboxylation. Furthermore, when exploring the remaining non-smoked parts of the joint, it was observed that the THC levels in those closest to the lit end were consistently higher than in the control samples. Specifically, the middle and upper-middle sections of the joint showed a notably greater concentration of total THC.


The investigation then extended to the residues after most of the joint was smoked. Here, after ¾ of the joint was smoked, the ¼ left over was not only elevated in THC levels but also certain terpenes like linalool and caryophyllene were found in higher concentrations. A closer look at the terpene profile revealed interesting patterns. After smoking just ¼ of the joint, the remaining lower sections retained higher concentrations of various terpenes compared to the upper sections.


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