How Cannabis Use Affects Your Brain After 40

As of June 2022, 37 US states have passed medical cannabis laws and 19 states have legalized recreational cannabis. Cannabis has proven beneficial for a range of conditions such as childhood seizure disorders, nausea, vomiting, and loss of appetite in people with HIV/AIDs.

Recently, a new generation of cannabis products has exploded onto the scene, driven by marketing that fuels a multi-billion dollar industry.

Interestingly, the average content of THC (tetra-9-tetrahydrocannabinol, the psychoactive and potentially addictive chemical in cannabis) in smoked whole-plant products has risen from 1% to 4% in the 1970s to 15% to 30% from today’s cannabis dispensaries. In addition, edibles and vapes may contain even higher concentrations of THC.

It seems there is an increase in public perception that cannabis is a harmless substance, but the long-term benefits and risks of cannabis remain unclear.

Recent evidence indicates that one consistent pattern has emerged: heavy long-term cannabis use can impact midlife cognition.

What is the evidence telling us?

Recent research published in The American Journal of Psychiatry closely followed nearly 1,000 individuals in New Zealand from age 3 to age 45 to understand the impact of cannabis use on brain function⁽¹⁾.

The longitudinal design enabled comparison of a person’s midlife cognitive abilities to their childhood cognitive abilities prior to using cannabis. In addition, this research enabled to ascertain the role of hippocampal gray matter volume in mediating associations between long-term cannabis use and cognitive deficits.

There are 5 major findings from this research:

1. Long-term cannabis users (several years or more) and heavily (at least weekly, though a majority in their study used more than four times a week) demonstrated IQ decline and inferior learning and processing speed in midlife relative to their childhood IQ.  People who were well acquainted with them described them as having memory and attention problems.  
2. Long-term cannabis users demonstrated significantly larger IQ decline, poorer learning and memory, and inferior processing speed than long-term tobacco or alcohol users. IQs declined by 5.5 points on average from childhood. The more frequently an individual used cannabis, the greater the resulting cognitive impairment, suggesting a potential causative link. Contrary to some claims, cognitive deficits were more pronounced for long-term cannabis users than for long-term tobacco or alcohol users⁽²⁾.
3. Cognitive functioning among midlife recreational cannabis users was similar to representative cohort norms, implying that infrequent, non–problem recreational cannabis use in midlife is unlikely to compromise cognitive functioning.
4. Cannabis quitters showed subtle cognitive deficits that may explain inconsistent findings on the benefits of cessation⁽³⁾.
5. Long-term cannabis users showed smaller volume in total hippocampus and five of 12 structurally and functionally distinct subregions compared with nonusers⁽⁴⁾.

The implications of this study are that long-term cannabis use is robustly associated with cognitive deficits in midlife.

These may be consequential given that mild cognitive deficits in midlife are a risk factor for dementia⁽⁵⁾.  

More research is needed to ascertain whether long-term cannabis users show elevated rates of dementia in later life.

This is crucial given the huge burden of dementia, and it is timely given the confluence of two trends: the growth of the aging population, and the record high rates of cannabis use among today’s older adults.

So, what actions can you take if you experience cognitive effects of cannabis?

Long-term users of cannabis may potentially develop brain fog, lowered motivation, difficulty with learning, or difficulty with attention. Symptoms are typically reversible, though using products with higher THC content may increase risk of developing cognitive symptoms.

If you are experiencing cannabis-related cognitive symptoms, consider the following:

• - Try a slow taper. Gradually decrease the potency (THC content) of cannabis you use or how frequently you use it over the course of several weeks, especially if you have a history of cannabis withdrawal.
• - Work with your clinician. Be honest and open with your clinician about your cognitive symptoms, as other medical or psychiatric factors may be at play. Your clinician can also assist you with navigating a cannabis taper safely, and potentially more comfortably, using other supportive means.
• - Give it time. It may take up to a month before you experience improvements after reducing your dose, as cannabis can remain in the body for 2-4 weeks.
• - Try objective cognitive tracking. Use an objective means such as an app or a test such as the mini-mental status exam to track your brain function. This may be more accurate than self-observation, which is quite subjective. Your mental health provider may be able to assist with administering occasional cognitive assessments.
• - Consider alternative strategies. Brain function is not static, like eye color or the number of toes on our feet. Aerobic exercise, strength training and engaging in mindfulness, meditation, and psychotherapy may improve long-term cognition.

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References:
1.    Meier, M.H., et al., Long-Term Cannabis Use and Cognitive Reserves and Hippocampal Volume in Midlife. Am J Psychiatry, 2022. 179(5): p. 362-374.
2.    Bourque, J. and S. Potvin, Cannabis and Cognitive Functioning: From Acute to Residual Effects, From Randomized Controlled Trials to Prospective Designs. Front Psychiatry, 2021. 12: p. 596601.
3.    Lovell, M.E., et al., Cognitive outcomes associated with long-term, regular, recreational cannabis use in adults: A meta-analysis. Exp Clin Psychopharmacol, 2020. 28(4): p. 471-494.
4.    Lorenzetti, V., et al., Does regular cannabis use affect neuroanatomy? An updated systematic review and meta-analysis of structural neuroimaging studies. Eur Arch Psychiatry Clin Neurosci, 2019. 269(1): p. 59-71.
5.    Gonzalez, H.M., et al., Midlife cardiovascular health and 20-year cognitive decline: Atherosclerosis Risk in Communities Study results. Alzheimers Dement, 2018. 14(5): p. 579-589.