A groundbreaking study in Amsterdam reveals that adult cannabis use shows no greater cognitive decline than non-users, defying long-held assumptions about the effects of weed on intelligence.
A recent study conducted in Amsterdam has found that the age at which men start smoking cannabis has no negative bearing on cognitive decline later in life. Contrary to the long-held assumption that weed makes you dumb, this research suggests that frequent adult cannabis use shows no greater cognitive decline in the long term than non-users.
The Study’s Key Findings
The study, which surveyed 5,162 men born between 1949 and 1961, found that those who started smoking cannabis at an older age experienced less mental decline than those who began using it earlier. In fact, the researchers discovered a slight reduction in cognitive decline among smokers compared to non-users, amounting to a difference of ‘1.3 IQ points’.
Cannabis, also known as marijuana, has been used for medicinal and recreational purposes for thousands of years.
Research suggests that cannabis contains over 100 different chemical compounds called cannabinoids, which interact with the brain and body in various ways.
THC, the primary psychoactive compound, can produce feelings of 'euphoria' and relaxation, while CBD, a non-psychoactive compound, has been shown to have potential therapeutic benefits for pain relief and inflammation reduction.
Studies also indicate that long-term cannabis use may be linked to cognitive impairment, memory loss, and increased risk of mental health disorders.

Limitations and Future Research Directions
While this study is not definitive, its findings align with other research that has found no significant age-based cognitive decline associated with cannabis use. The Danish study’s exclusion of women is a notable limitation, as the same test was used on both participants and those who averaged ’44 years older’ . Future research could investigate whether the lack of long-term cognitive effects in cannabis users lies in underlying factors such as socioeconomic class or if the results are specific to weed use itself.
The War on Marijuana: A Misguided Effort
The anti-cannabis studies that have been used to justify the ‘War on Marijuana’ have been widely discredited, with many being funded by pharmaceutical giants and right-wing think tanks. These studies have failed to reduce pot use and have allowed police to exercise racial bias throughout minority communities. Building on this Danish study, future research can help shed light on the true effects of cannabis use and inform more effective policies in the future.
Marijuana prohibition began in the United States with the passage of the Marihuana Tax Act of 1937.
The act imposed a tax on the sale of marijuana, effectively regulating its use and distribution.
However, it was the Controlled Substances Act of 1970 that classified marijuana as a Schedule I substance, alongside heroin and LSD.
This classification restricts research and limits access to medical marijuana.
According to the American Civil Liberties Union (ACLU), over 600,000 people were arrested for marijuana possession in 2012 alone.