Anti-drug campaigns warn that marijuana causes memory loss, especially in young consumers. But some studies suggest that cannabis can protect the brain against the memory deficits caused by Alzheimer’s disease. Many people who consume cannabis also say that it promotes better concentration and focus. So, which is true—does cannabis improve or impede memory?
After decades of intensive research on the effects of cannabis consumption on memory, the answer to that question is that it can do both—or neither. Marijuana’s effects on memory are complex and contradictory. The picture is complicated by variations in study methods, and by the many different processes that make up what we call memory.
Memory is usually understood as the ability to recall past events or information. But the processes that make this possible are distributed throughout the brain and involve input from many different neural pathways. Since memory involves processing and storing input we receive from multiple sources, those various pathways are activated depending on the nature of the incoming information. Information received through the sense of smell, for example, is processed differently than information that’s seen or heard.
In general, memory is a four-step process that includes receiving, processing, learning and storing information. But [many different areas of the brain activate](https://www.researchgate.net/publication/16888995_Cannabis_Effects_on_memory_and_the cholinergic_limbic_system) in order to do that, including the:
Research has defined several different types of memory arising from activity in those areas, such as short- and long-term memory, visual, spatial and verbal memory. There are even other types of memory that are combinations of these, such as spatiovisual memory.
There’s also a special category for executive functions—the combination of learning, memory and cognitive processing. This all takes place in the prefrontal cortex that lets us make decisions, choose between options and evaluate situations.
Areas of the brain most responsible for memory are rich in the endocannabinoid receptor CB1, too. And this accounts for the many different effects cannabis can have on memory processes.
For decades, marijuana has been blamed for killing brain cells and causing consumers to go through life stoned and stupid. While that’s an exaggeration, numerous studies do show that cannabis, especially strains high in tetrahydrocannabinol (THC), can cause short-term memory. THC binds to CB1 receptors in the brain that are responsible not only for mood, but also for memory and cognition. This explains the short-term memory deficits that can go along with being high.
These memory problems usually resolve themselves once cannabis is processed out of the body. But the effects can linger because various cannabis compounds are metabolized at different rates. So anyone who consumes marijuana very frequently or heavily can appear to be having long-term or permanent memory problems, when it’s more likely that THC hasn’t yet been flushed from the body.
Memory deficits from cannabis may be largely transitory, but a growing body of research does confirm that teen cannabis users are at greater risk for memory loss that persists. That’s because the human brain is still developing until the age of 25 or so. As well, teen brains are in many ways very different from adult brains. Among teens, high-THC strains of cannabis can affect the connectivity among these developing neural networks, so that they don’t have the opportunity to mature normally.
Cannabidiol (CBD), the other compound found abundantly in cannabis, has little to no psychoactive effects. CBD affects immune-related processes and cell health, so that it can:
Cannabis has potent properties as a neuroprotectant, and CBD is largely the reason. CBD can support the growth of healthy nerve cells, but also slow or prevent the development of abnormal cells and other toxic substances.
Because CBD protects nerve cells, it can help relieve symptoms of progressive neurological disorders like Parkinson’s disease. Some studies have shown that for the same reasons, it can protect the brain’s memory pathways from damage caused by beta-amyloid plaque—the sticky protein believed to be the cause of Alzheimer’s disease. Other research reveals that marijuana products high in CBD may also help to protect and support memory functions after traumatic brain injury or stroke. In people who don’t have these conditions, high-CBD cannabis may also help with concentration and focus.
One reason that it’s difficult to come to a definitive answer about the effects of cannabis on memory is that much of the research itself produces ambiguous results. Because memory encompasses so many different functions and areas of the brain, different studies base their results on different kinds of tests.
While one team may ask volunteers to take a verbal memory test such as reciting back words they’ve memorized, another might ask study subjects to recall details in a picture. These tasks activate a completely different memory pathway.
Most research also relies on self-reporting from subjects about how—and how much—marijuana they consume. And those reports may not be accurate or consistent. Variations in things like an individual’s overall health and even the number of cannabinoid receptors they have can also play a role in how cannabis affects memory.
The effects of marijuana on memory have been studied intensively for several years, with widely varying results. But because cannabis can affect all kinds of processes in the body, it’s clear that it can affect memory, too—in both positive and negative ways.
Photo credit: Michael