A recent study has shown that cannabis and tobacco use can alter brain structure and reduce the size of specific areas within it.
Whether used alone or together, these substances accumulate over time, potentially leaving long-lasting effects on thinking, feelings, and daily performance.
The study indicated that regular cannabis users often have a smaller amygdala, a brain region that plays a key role in regulating emotions and the body's threat response. Tobacco use, on the other hand, has been linked to broader brain changes, including shrinkage of the amygdala, the insula (which controls self-awareness and emotions), and the globus pallidus (responsible for movement and neural stimulation).
As the years go by, these changes become more pronounced; smokers, compared to non-smokers, show a faster decline in the volume of gray matter, which is a key indicator of brain health and is linked to mental performance and psychological well-being.
The researchers analyzed more than 103 studies involving 72,000 people using several methods:
Comparing users and non-users at a single point in time.
Following the same people for years to monitor changes.
Using genetic data to understand the relationship between substance abuse and brain changes.
The results showed that cannabis and tobacco use is associated with shrinkage of key brain regions, such as the amygdala, insular cortex, globus pallidus and hippocampus, which are responsible for memory and learning.
Number of those affected and the impact of the materials
It is estimated that around 228 million adults worldwide use cannabis, while approximately 1.8 billion people smoke tobacco, representing about 30% of the world's population. This habit causes more than 8 million deaths annually.
The main psychoactive compound in cannabis is THC, which affects the brain via specific receptors that control pain, anxiety, and appetite. Nicotine in tobacco, on the other hand, works via neural receptors that control communication between nerve cells and the brain's ability to learn and adapt.
By precisely identifying these areas, healthcare professionals can provide clearer information to patients, especially young people and high-risk groups, about how cannabis and tobacco affect their brain and long-term health, rather than general and vague warnings.
The study was published in the journal Addiction.
