Marijuana’s Memory Paradox

Are pot smokers less likely to get Alzheimer’s? A compound similar to the active ingredient in cannabis shows promise as a potential memory protector.
By Maia Szalavitz for MSN Health & Fitness
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Marijuana isn’t known for being a friend to memory; its short-term effects notoriously impair recall. And although the data is conflicting, some studies link cannabis with memory deficits in those who use excessive doses for long periods of time

But new research suggests that one of the active ingredients in marijuana—THC—and similar compounds could possibly prevent or even reverse one of the most devastating memory disorders of all: Alzheimer’s disease.

In a paper published in the December 2008 issue of the journal Neurobiology of Aging, researchers found that a compound that affects the same brain receptors as THC reduced brain inflammation and improved memory in older rats. (The rodents were the human equivalent of age 65 to 70.) Although there’s debate over the role played by inflammation in Alzheimer’s, many researchers believe it’s an important part of the process that causes dementia.

"We were shocked and surprised that it worked," says Gary Wenk, Ph.D., one of the study’s authors and a professor of psychology and neuroscience at Ohio State University. 

Wenk and his colleagues traced the anti-inflammatory effect of the compound (which has the awkward name "WIN-55,212-2") to its activation of cannabinoid receptors on brain cells—the same receptors activated by THC.

Other anti-inflammatory compounds studied in rats and humans like NSAID drugs (ibuprofen, etc.) showed effects on young brains, but unlike WIN-55,212-2 did not improve aged brains.

Wenk has also found in these older rats that the  WIN-55,212-2 compound promotes the growth of new brain cells—a process that declines and may even stop in older animals. "The most amazing thing we saw was that it re-initiates neurogenesis—usually, the only drugs that do that are the SSRI antidepressants [selective serotonin re-uptake inhibitors, the class of drugs that includes Prozac]."

Timing is everything

How could a drug that clearly impairs memory while people are under its influence function to protect users’ recall in the long term? Wenk theorizes that this could be due to differences in the way young and old brains learn.

Research shows that the neurotransmitter glutamate is involved in storing memory in a process that involves growing both new cells and connections between them, and destroying old ones. Some current Alzheimer’s drugs like memantine affect glutamate—as does THC.

Early in life, this process is in balance, and so interfering with either the growth or the "pruning back" of brain cells and connections—as might occur from using marijuana—might impair memory. But, says Wenk, "The same systems involved in pruning neurons at the beginning of life could be killing them at the end." Therefore, interfering with the pruning process later in life might actually help, rather than harm.

No need for a high

Rest assured, Wenk and his colleagues aren’t advocating a stoner lifestyle.

Because WIN-55,212-2, like THC, produces a high, the researchers looked for the lowest effective dose. They estimate that that dose is the equivalent to just one toke of marijuana. "A puff is enough," Wenk says.

Though that dose wouldn’t get someone high, it could, admittedly, have some psychoactive effect. But this wouldn’t necessarily rule out medical use. The drug could be taken before bedtime, for example. And with long-term use, tolerance to these psychoactive effects can develop, so impairment might be minimal with a steady dose anyway.

Marijuana’s Memory Paradox<