Smoking weed and tobacco accelerates brain shrinkage, say scientists

Researchers say cannabis and tobacco use is linked to reduced brain volume in key regions tied to emotions, memory, and movement, raising concerns about long-term brain health

The brain naturally shrinks as we age, but smoking tobacco and cannabis significantly speeds up this decline, researchers have found.

 

According to a new study titled Associations of cannabis use, tobacco use and co-use with brain volume: A systematic review and meta-analysis, published in the journal Addiction, smoking tobacco or cannabis shrinks key brain regions linked to emotions, memory, decision-making, and basic bodily awareness, and may contribute to faster-than-normal brain ageing.

 

The analysis, which draws data from over 72,000 people across more than 100 studies, led by scientists at King’s College London and the University of Bath, UK, says that cannabis use correlates with a smaller amygdala that regulates emotions like fear and anxiety, decision-making in risky situations, and survival instincts. Tobacco use is tied to volume loss across multiple areas, including the insula that governs body awareness (hunger, pain, cravings), the pallidum that controls voluntary movement and plays a role in emotional processing, and total grey matter, which is critical for thinking, memory, and decision-making. Loss in these regions may impact both physical coordination and mental health.

 

 

The researchers say that this may explain why some users experience heightened anxiety or impaired judgment over time.

Can higher smoking levels increase brain shrinkage risk?

The findings suggest a dose-dependent effect, especially with tobacco, where higher cigarette consumption reduces hippocampal volume. The hippocampus is crucial for memory and learning.

 

This means the more one smokes, the greater the potential impact on brain structure.

Why does smoking tobacco and cannabis affect brain structure?

Researchers point to the harmful effects of combustion, such as burning substances like tobacco or cannabis:

• Produces reactive oxygen species (ROS)
• Leads to oxidative stress and inflammation
• Triggers neuronal cell damage and death

The study authors say that the review primarily analyses regular or long-term use, so occasional use may not have the same impact. However, the findings raise concerns about cumulative exposure over time. They also warn that brain changes may develop gradually and go unnoticed.

What are the wider public health implications of these findings?

The researchers emphasise the need for:

• Stronger public awareness campaigns on brain health, not just lung health
• Doctors to discuss neurological risks alongside other harms
• Discouraging mixing tobacco with cannabis

The researchers say that the brain is not just ageing naturally, but may be shrinking faster in people who use tobacco and cannabis, and what feels like a temporary habit could be reshaping the brain permanently in the long run.