Reference: Mueller, R. L., Ellingson, J. M., Bidwell, L. C., Bryan, A. D., & Hutchison, K. E. (2021). Are the acute effects of THC different in aging adults? Brain Sciences, 11(5), 590.
Marijuana, pot, weed, dope, grass, cannabis, whatever you may call it, you have likely heard of the centuries-old plant that has become legalized either medically, recreationally, or both in many countries over the past decade. Cannabis, the plant’s scientific name, is composed of more than 400 chemicals, 60 of which are compounds called cannabinoids (Atakan, 2012). Unsurprisingly, with so many different chemicals and compounds, the effect of cannabis on humans remains fairly misunderstood. However, two cannabinoids have been well-researched: delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). THC, the main psychoactive compound in cannabis, affects functions of the nervous system (e.g., increased heart rate) and can cause changes in mood, perception, consciousness, cognition, and/or behavior (e.g., paranoia); CBD, on the other hand, has an opposing effect to THC such that it is not intoxicating and induces calming effects (e.g., heart rate reduction and/or paranoia; Karniol et al., 1975; Kicman & Toczec, 2020).
Most of the available research has focused on the effects of cannabis consumption, specifically THC, on adolescents (e.g., 15- 18 years old) and young adults (e.g., 20 – 25 years old; Lisdahl et al., 2014; Scott et al., 2018; Hall et al., 2020). But, as a result of the increase in global cannabis legalization, more people are consuming cannabis. Thus, it is important we understand how the drug affects human functioning across a variety of age ranges. To this end, Raeghan Mueller and colleagues at the University of Colorado Boulder compared the effects of consuming cannabis with different concentrations of THC and CBD, on thinking, feeling, and craving in younger adults compared to older adults.
How was the research study carried out?
Mueller and colleagues recruited eighty-six participants from Colorado (54 younger adults and 32 older adults) who had consumed cannabis at least four times per month for the previous six months, and within that time frame had consumed the highest concentrated THC cannabis strain (24% THC) that could be assigned in the study. The younger (21 – 25 years old) and older (55 – 70 years old) adults completed objective assessments (i.e., memory) and subjective assessments (i.e., mood, cravings) in two different sessions.
In the first session, they completed baseline assessments such as a demographics questionnaire, memory task, attention task, processing speed, flexible thinking, cannabis craving, and anxiety questionnaires. The researchers randomly assigned participants to consume high-THC, high-CBD, or balanced THC + CBD cannabis over five days however the participants wanted (e.g., consuming edibles, smoking, taking capsules, etc.) over the next five days.
Five days later, participants returned to the lab to see how the different cannabis strains affected their thoughts and feelings. There were three parts to this session: pre-use, immediate post-use, and delayed post-use. Pre-use meant before the participant had consumed cannabis that day. Immediate post-use was right after the participant smoked the cannabis strain that they were assigned – everyone was required to smoke their assigned cannabis strain for this part of the study. Delayed post-use occurred one hour after consuming cannabis. At pre-use, immediate post-use, and delayed post-use, participants completed the same assessments of memory, attention, processing speed, flexible thinking, cannabis craving, and anxiety questionnaires – the same testing that was performed five days prior.
What was found?
Younger adults’ memory was worse than older adults’ memory immediately after consuming high-THC cannabis. Similarly, the younger adults performed slower in a thinking task compared to older adults immediately after consuming high-THC cannabis and 1 hour after consuming high-THC cannabis. However, younger and older adults demonstrated similar attention and flexible thinking skills, regardless of the type of cannabis they consumed. The younger and older adults who consumed high-THC experienced the same amount of anxiety; however, older adults who consumed high-CBD cannabis experienced more anxiety 1 hour after consumption compared to younger adults who also consumed high-CBD cannabis. Younger adults craved cannabis more than older adults across all cannabis groups and times (see Figure 1).
Cannabis craving is higher in younger adults compared to older adults across cannabis groups and time points. High CBD group is in gray, high THC group is in pink, and balanced CBD+THC are in teal. The y-axis represents subjective craving of cannabis; a higher score represents a higher craving. The x-axis represents the older and younger adults at two different study time points (pre-use = 0’ and delayed post use=60’) across the different cannabis strain groups.. The asterisks (*) represents significant differences between two groups. Figure is courtesy of the research paper.
What does this all mean?
All in all, cannabis affected older and younger adults differently. First, as the authors predicted, younger adults in the high-THC group performed worse on the memory and processing-speed tasks after consuming high-THC compared to the older adults. This was an interesting finding because the younger adults reported using cannabis more and consuming higher THC-concentrated products. Given the younger adults’ experiences with THC, we might expect them to be less rather than more affected by cannabis consumption. However, the effects of THC differing by age may be explained by older adults feeling fewer of the psychoactive effects of THC because, as previous research has shown, there is a decrease in the number of cannabis receptors in the brain with increased age (de Oliverira et al., 2019; Leishman et al., 2018; Mato & Pazos, 2004). With fewer cannabis receptors in the brain, older adults may experience less effects from THC consumption (e.g., change in consciousness) than younger people, such as hindering their ability to carry out tasks.
Additionally, it was unanticipated that CBD would lead to greater anxiety in older compared to younger adults given that CBD is typically advertised as the calming cannabinoid (Karniol et al., 1975). This finding suggests that CBD may have some anxiety-provoking qualities in older adults, but further research is required. Moreover, it was also interesting to see that the older adults in the high-CBD group had greater anxiety compared to the older adults in the THC + CBD group. The reasoning for these findings is unclear, but it should be noted that there were only 9 older adults in the high-CBD group compared to 17 younger adults. A replication study with more participants in each cannabis group would help address whether these results are reliable.
Lastly, as expected, younger adults expressed a higher craving for cannabis than older adults. However, this finding may have occurred because earlier cannabis use is linked to greater cannabis dependence (Degenhardt et al., 2008) and the younger adults reported being younger when they began to regularly use cannabis (average of 17 years old when they began) compared to older adults (average age of 27 years old when they became regular users).
Where to go from here?
Cannabis affects older and younger adults differently – and in surprising ways! High-THC cannabis seems to more negatively affect memory and processing speed in younger adults compared to older adults, even though younger adults tend to perform similarly to older adults on these types of tasks when sober. High-CBD cannabis, on the other hand, may lead to higher anxiety in older adults when compared to younger adults, even though CDB is typically consumed to decrease anxiety.
Therefore, marijuana, pot, weed, dope, grass, cannabis, regardless of what it’s called, there is clear evidence that it can have different effects on thoughts and feelings in adults depending on one’s age. This study was an important step in closing the gap between the misunderstood and the understood effects of cannabis consumption on human functioning. However, future research is warranted to fully grasp the different effects that cannabis may have on the brain and behavior, especially long-term effects in regular cannabis users.
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