Long Term Effects of Cannabis on Cognition
Current Research on the Long-Term Effects of Cannabis on Memory and Cognition
Cannabis is a medicinal plant that has been shown to improve a wide range of symptoms including childhood seizure disorders, nausea, vomiting and loss of appetite in people with HIV/AIDS.
As cannabis use becomes more common (both medicinally and recreationally), it's important to look beyond its short-term effects and consider how long term use may influence brain health as we age. Recent evidence highlights the need for thoughtful, informed use, especially for those who use cannabis frequently or over many years, however, definitive long term benefits and risks of cannabis remain unclear.
What does the research say?
A large, long term study recently published followed nearly 1000 individuals in New Zealand from early childhood (age 3) to midlife (age 45). The findings suggest that long-term, heavy cannabis use, defined as weekly or more frequent use for several years, can negatively impact brain function. Specifically, individuals with this pattern of use showed:
A decline in IQ averaging 5.5 points from childhood levels
Slower learning ability and reduced processing speed compared to non-users
Noticeable memory and attention problems
These effects appeared stronger with heavier, more frequent cannabis use. Interestingly, cannabis-related cognitive impairment appeared to be greater than that seen with long-term alcohol or tobacco use.
Neurologically, heavy cannabis users were found to have smaller hippocampi which is the part of the brain involved in memory and learning. In contrast, people who used cannabis occasionally (less than once a week) and did not develop dependence did not show these cognitive deficits. This points to a possible threshold where risk increases.
Broader evidence on cannabis and cognition
Beyond this study, there is strong research in the literature that THC or cannabis impairs verbal and non-verbal learning and episodic memory in current heavy users. Their effects are greater with higher doses, earlier onset of use and longer duration of use. There is also evidence that cannabis can also impair attentional control, particularly sustained and divided attention in heavy users. The good news is, research shows that memory and attention can start to improve after stopping cannabis use, especially for those who use it less frequently and for a shorter duration.
In general, heavier and longer term use of cannabis, especially starting at a younger age seems to be linked to more lasting challenges with thinking and memory in midlife. But these effects may ease once cannabis use stops, particularly in people who used it less frequently. While these studies add to growing evidence of a link between long-term heavy cannabis use and cognitive decline, more research is needed to fully understand the long-term risks.
Cannabis can offer therapeutic benefits, but like any treatment, it’s important to weigh both its potential advantages and risks. If you’re using cannabis or considering it for health reasons, our team of naturopathic doctors, psychotherapists, and other integrative care providers can help you make choices that support your cognitive health and overall well-being.