Anyone who has ever eaten one too many space cakes will testify to the fact that cannabis generally behaves in a dose-dependent manner, meaning the more you consume, the more stoned you get. However, a new study in the journal JAMA Psychiatry[i] suggests that this may not necessarily have anything to do with THC, and that there might even be a limit to how much THC a person can ingest before it stops having any additional effect.
Study participants were given either cannabis flower, with a maximum THC content of 24 percent, or high-potency cannabis concentrates containing up to 90 percent THC. Unsurprisingly, those who used the concentrates were then found to have much higher amounts of THC in their blood, with levels peaking at 1,016 micrograms per millilitre a few minutes after use, compared with 455 micrograms per millilitre for those who smoked bud.
However, the results of numerous tests indicated that those participants with the highest concentrations of THC in their blood were no more stoned that those with the lowest levels of plasma THC. This was first corroborated through subjective reports, as both groups described experiencing equal effects, with the same types and magnitudes of changes to their mood and perception.
The two groups also performed equally on memory impairment tests, including one where they were asked to memorise a shopping list for thirty minutes. Other tasks designed to measure balance found that both groups experienced an 11 percent decrease in their equilibrium.
“Surprisingly, we found that potency did not track with intoxication levels,” said study author Cinnamon Bidwell in a statement. “While we saw striking differences in blood levels between the two groups, they were similarly impaired.”[ii]
The researchers can’t say for sure why this was the case, though they speculate that “cannabinoid receptors may become saturated with THC at higher levels, beyond which there is a diminishing effect of additional THC”. In other words, once your receptors are full of THC, there’s no point in consuming any more as it simply has nothing to bind to.
It’s worth noting that all of the participants in this study were regular cannabis users and may therefore have built up a tolerance to THC over time, which might provide an alternative explanation for these findings. It’s also important to consider that this research contradicts a previous study in which people who smoked joints containing 69 mg THC were considerably more stoned than those who only smoked 29 mg THC.[iii]
Then, of course, there’s the aforementioned space cake crisis that so many of us have had to navigate at some point in our lives. If THC stops having an effect once a certain level has been reached, then how can eating too much special confectionary produce such an epic couch lock?
The answer may be less to do with THC per se, and more to do with the mode of ingestion.
When smoked, THC passes straight out of the lungs and into the blood, where it can’t really dissolve or be metabolised that efficiently, so it winds up just binding to the nearest cannabinoid receptors. Yet it’s a whole different story with edibles, which bring THC into contact with the gut and the liver. Here it is broken down into 11-hydroxy-THC, which is more soluble in blood and much better at crossing the blood-brain barrier than regular THC. As a result, edibles often produce a more intense effect than smoking does, though it generally takes much longer for this high to kick in.
Furthermore, if the brain’s cannabinoid receptors can only accommodate a limited amount of smoked THC, there’s no limit to how much weed can be digested by the gut, which could explain why you don’t stop getting more stoned when you eat more weed. However, more research is needed before conclusions like this can be drawn with any certainty.
While we’re on the subject, studies have also found vaping to produce a stronger effect than smoking[iv]. This is probably because smoking generates very high temperatures, which means some of the cannabinoids get burned. In contrast, vaping temperatures are optimised to ensure that cannabinoids become decarboxylated – a process that is necessary before they can produce a psychoactive effect – without burning. According to one study, vaping at 200 to 230 degrees Celsius releases the maximum amount of cannabinoids, though smoking generally generates much higher temperatures than this[v].
Of course, THC isn’t the only component of marijuana that produces a high, and there are plenty of other cannabinoids and terpenes that factor in as well – so perhaps it’s not that surprising that blood THC levels don’t entirely correlate with intoxication levels.
[i] L. Cinnamon Bidwell, Jarrod M. Ellingson, Hollis C. Karoly, Sophie L. YorkWilliams, Leah N. Hitchcock, Brian L. Tracy, Jost Klawitter, Cristina Sempio, Angela D. Bryan, Kent E. Hutchison. Association of Naturalistic Administration of Cannabis Flower and Concentrates With Intoxication and Impairment. JAMA Psychiatry, 2020; DOI: 10.1001/jamapsychiatry.2020.0927
[iii] Hunault, C.C., Böcker, K.B.E., Stellato, R.K. et al. Acute subjective effects after smoking joints containing up to 69 mg Δ9-tetrahydrocannabinol in recreational users: a randomized, crossover clinical trial. Psychopharmacology 231, 4723–4733 (2014). https://doi.org/10.1007/s00213-014-3630-2
[iv] Malouff JM, Rooke SE, Copeland J. Experiences of marijuana-vaporizer users. Substance abuse. 2014 Apr 3;35(2):127-8. – https://www.tandfonline.com/doi/abs/10.1080/08897077.2013.823902
[v] Pomahacova B, Van der Kooy F, Verpoorte R. Cannabis smoke condensate III: the cannabinoid content of vaporised Cannabis sativa. Inhalation toxicology. 2009 Nov 1;21(13):1108-12. – https://www.tandfonline.com/doi/abs/10.3109/08958370902748559