New research suggests smoking cannabis and tobacco can leave a physical mark on the brain.
With 420 around the corner, some people may be getting ready to mark the occasion by smoking a joint, despite the long-standing warnings about the harms linked to smoking.
Studies have also challenged the idea that the devil’s lettuce is harmless. Reported downsides range from disrupted sleep and irritated airways to, as the Cleveland Clinic states, lower life achievements.
Brain volume tends to decline as we get older, but smoking can speed up that reduction — a change associated with a higher likelihood of cognitive problems over time.
Now, a fresh review indicates marijuana and tobacco use may be tied to measurable shrinkage in specific brain regions.
Published in the journal Addiction, the analysis pulled together findings from multiple studies examining cannabis use, tobacco use, and using both. Across the evidence, researchers reported that cannabis and tobacco use were each associated with reduced amygdala volume.
The amygdala is small but crucial, helping regulate emotion, fear and survival responses, and supporting memory and learning. A smaller amygdala has been linked to difficulties with emotional control, heightened anxiety, emotional blunting, and reduced ability to recognise fear — factors that can contribute to riskier choices.
Tobacco use was also associated with lower volume in the pallidum and insula. The pallidum, found deep within the brain, is important for voluntary movement control and for handling emotions tied to motivation, risk, and reward.”
When the pallidum shrinks, it’s often discussed in the context of neurodegenerative conditions such as Huntington’s and Alzheimer’s disease, which can involve both movement-related and thinking-related symptoms.
The insula, meanwhile, helps track internal signals such as hunger and pain and contributes to feelings, cognition, and self-awareness.
The review also reported that regular cigarette smoking was linked with lower total grey matter, which plays a role in processing senses, controlling muscles, and making decisions. Smoking more cigarettes per day was strongly associated with smaller hippocampal volume — a region central to learning, memory, spatial navigation, language, and recalling experiences. Because hippocampal shrinkage is often treated as an indicator of dementia and cognitive decline, researchers pay close attention to changes in this area. Many of these regions interact closely, with the amygdala and hippocampus working together to connect emotion and memory in shaping responses.
Cannabis refers to the plant species containing both THC — the compound responsible for a ‘high,’ — and CBD, a non-intoxicating compound believed to have antioxidative and anti-inflammatory properties.
In related research, a separate study outlined the surprising changes that can occur in the body after a single puff of a cigarette.
If you need support and advice about quitting smoking, go to the American Lung Association’s ‘Freedom from Smoking’ website where you can access resources and speak to professionals.