In the UK, medical cannabis flower is prescribed to be consumed via vaporisation. However, smoking is the most common way cannabis flower is consumed globally.
The main reason the smoking of medical cannabis is not permitted in the UK is because burning cannabis for smoking can produce cancer-causing compounds and other compounds which negatively affect the lungs and the heart. In addition, the smoking of medical cannabis is prohibited by the Misuse of Drugs Regulations 2001.
However, very little was previously known about how smoking cannabis affected the delivery of cannabinoids except for tetrahydrocannabinol (THC). The authors of a recent study aimed to shed light on the changes that occur within a cannabis cigarette as it’s smoked. The research reveals that the delivery of cannabinoids and terpenes is not uniform throughout the smoking process, and the composition of the inhaled smoke changes as the cigarette burns down.
What is Contained within Cannabis?
The effects of cannabis are largely determined by its active ingredients: cannabinoids like THC and cannabidiol (CBD). Terpenes, the aromatic compounds that give cannabis its unique aroma, may also contribute to its effects.
More than 140 cannabinoids have been identified in cannabis. Cannabinoids predominantly appear in cannabis flower in their acid form and decarboxylate to the neutral form when heated.
Cannabis also contains more than 200 terpenes, of which about 20 are the most prevalent.
Studying How Smoking Affects Cannabis Composition
Previous studies have shown that smoking cannabis results in a relatively low yield of cannabinoids. This is because up to 50% of cannabinoids are lost in side-stream smoke, while up to 30% are destroyed by too high temperatures and 10% are trapped in the butt. Moreover, terpenes, with their lower boiling points, evaporate before cannabinoids like THC.
The study therefore focused on:
Reproducibility: Can smoking a cannabis cigarette (a joint) consistently deliver the same amount of cannabinoids and terpenes in different portions?
Variation: Is there a difference in the delivery of cannabinoids and terpenes when smoked?
Mechanism: What explains the observed results?
Methods
The researchers conducted ten experiments, studying changes in cannabinoids and terpenes during smoking, using a specialist smoking machine. Cannabinoid and terpene content was evaluated using high-performance chromatography analysis of the cannabis cigarettes’ residuals and the smoke composition.
Key Findings
Uneven Distribution: The study found that cannabinoid levels, particularly THC, increase in the sections of the cigarette closer to the mouth (the unsmoked end) compared to the lit end. This suggests that cannabinoids are volatilised by the heat at the burning end and then condense and accumulate further down the cigarette.
Increasing Potency: As a result of this accumulation, the amount of cannabinoids delivered per puff increases as the cigarette is smoked. This means that the last few puffs may be significantly more potent than the first few.
Terpenes First: Terpenes, being more volatile than cannabinoids, are inhaled earlier in the smoking process. This could influence the overall experience, as terpenes are thought to interact with cannabinoids to modulate their effects.
The Mechanism
The researchers propose a mechanism to explain these findings:
Decarboxylation and Evaporation: Heat from the burning end causes cannabinoids to decarboxylate (become active) and evaporate.
Vapour Migration: The vapourised cannabinoids travel away from the hot zone towards the cooler end of the joint.
Condensation: As the vapour cools, it condenses into small droplets that can be trapped within the cigarette’s structure.
Re-evaporation: As the burning zone progresses, these trapped cannabinoids re-evaporate and are inhaled in the smoke.
How Does This Compare to Vaporisation?
The same research group previously published another recent study which examined how vaporisation affects the chemical composition of cannabis flower.
Comparing the findings of these two studies, it becomes evident that vaporisation offers several advantages over smoking when it comes to the administration of medical cannabis, in addition to avoidance of the harmful byproducts. These include:
Preservation of Cannabinoids and Terpenes: The study on smoking demonstrates that the high temperatures involved in smoking lead to uneven distribution and potential degradation of terpenes and cannabinoids. In contrast, vaporisation, which operates at lower temperatures, allows for better preservation of these compounds. The exact ratio of compounds released during vaporisation can be influenced by changing the temperature within the recommended parameters.
As terpenes are more volatile compared to cannabinoids these evaporate much more quickly and are inhaled much earlier in both smoking and vaporisation. This difference in delivery could have implications for the entourage effect, as the interaction between these compounds might be influenced by the different timing of delivery.
Dose Control: The smoking study reveals that the concentration of cannabinoids in the inhaled smoke increases as the cigarette is consumed, making dose control challenging. Vaporisation, on the other hand, offers more consistent and predictable delivery of cannabinoids and terpenes, allowing for better dose control, which is crucial for medical cannabis users.
Why This Matters for Medical Cannabis Patients
These findings have significant implications for medical cannabis users who rely on consistent dosing for their treatment. Smoking cannabis cannot guarantee a uniform delivery of cannabinoids or terpenes, even within the same joint with lower doses to begin with and higher doses at the end. This is in addition to the loss of cannabinoids and terpenes in side-stream smoke and the destruction by too-high temperatures.
Conclusions
These findings indicate that smoking as a means of cannabinoid and terpene administration cannot be relied upon for the delivery of medical cannabis due to its inherent variability even within the same cigarette. The findings from this research group collectively suggest that vaporisation is a preferable method for medical cannabis patients. It offers better preservation of cannabinoids and terpenes, improved dose control, and potential harm reduction compared to smoking. This is in addition to the fact that smoking of medical cannabis is still prohibited under the Misuse of Drugs Regulations.
