New research suggests that smoking weed could age your brain by as much as three years.
Basically, if the new science is to be believed, consuming marijuana speeds up the ageing of the brain by around 2.8 years, which is worse than bipolar disorder or attention deficit hyperactive disorder.
However, schizophrenia ages the brain by an even greater amount of four years.
Drinking alcohol was also found to age the brain by 0.6 years.
The ageing of the brain is defined by the reduced amount of blood flowing through the organ.
The study shines a new light on the effects of smoking cannabis and the author of the study thinks that it should give us reason to think about how harmful it is.
Lead author Dr Daniel Amen said: "The cannabis abuse finding was especially important, as our culture is starting to see marijuana as an innocuous substance. This study should give us pause about it."
Reduced blood flow through the brain can cause health complications such as strokes and dementia.
The research used a large set of data compiled from 62,454 scans on the brains of 31,227 people.
The scans were performed during periods of concentration and rest on people aged between nine months old and 105 years old.
They were trying to establish factors that contribute to and define brain ageing.
Basically, the scientists analysed the blood flowing through 128 different regions of the brain and then used that data to determine the age of the person whose brain they were looking at.
Once they were actually told how old the person was, they could make an assessment of how accelerated the brain ageing process was.
Dr George Perry, from the University of Texas in San Antonio, said: "This is one of the first population-based imaging studies, and these large studies are essential to answer how to maintain brain structure and function during ageing."
Dr Amen continued: "Based on one of the largest brain imaging studies ever done, we can now track common disorders and behaviours that prematurely age the brain.
"Better treatment of these disorders can slow or even halt the process of brain ageing."
Another of the study's authors, Sachit Egan from Google, said: "The results indicate that we can predict an individual's age based on patterns of cerebral blood flow."
"Additionally, groundwork has been laid to further explore how common psychiatric disorders can influence healthy patterns of cerebral blood flow."