You must be 21 years old and above to access RxLeaf

Is Cannabis Shrinking Your Hippocampus? What Does This Mean For Your Long Term Health?

Randy Robinson
cannabis, medical cannabis, recreational cannabis, CBD, THC, cannabinoids, hippocampus, memory loss, regeneration, seizures, depression

Study says that THC shrinks the hippocampus, which puts patients at risk for depression and memory loss over the long term. Here’s why we say, “Don’t worry about that.”

According to a new study in Cannabis and Cannabinoid Research (2018), cannabis shrinks a region of the brain known as the hippocampus. The hippocampus is responsible for regulating memory, spatial navigation, and conflict avoidance. There’s also some evidence that the hippocampus could regulate neurogenesis. This is the regrowth of brain and nerve cells, however recent studies may contradict that claim.

cannabis, medical cannabis, hippocampus, recreational cannabis, neuron, brains, brain regions, research, cannabinoids, studies

Image credit: Sebastian Kaulitzki

In the Cannabinoid Research study, researchers at the University of California-Los Angeles used high-resolution MRI to scan the hippocampi of twenty four “former heavy CB users” and found the subjects’ hippocampal subregions were slightly but significantly thinner compared to twenty six controls who “reported never using CB or other illicit substances.”

How slight but significant? In the thickest subregion, about half a millimeter thinner. In the other subregions, the differences were about 0.01 to 0.1 millimeter thinner.

cannabis, medical cannabis, recreational cannabis, hippocampus, brain, neurons, brain regions, seizures, medication, research

Image credit: Brandon Crawford

But I Smoke Weed Everyday, and I’m Smart

Why should we care? After all, Carl Sagan smoked cannabis, and he hosted Cosmos.

Hippocampal shrinking has been documented in other subjects besides pot smokers. Reduced subregion volume also occurs in patients who suffer from recurring seizures and/or chronic depression.

Seizure patients live with a higher suicide risk due to depression. This is why some doctors worry about them consuming cannabis to control seizures. It’s possible that experiencing seizures and depression causes the hippocampus to lose volume. This diminished volume may lead to greater incidences of both seizures and depression symptoms. Thus trapping the patient in a feedback loop that carries the risk of premature death. As the hypothesis goes, if seizures shrink the hippocampus, and so does cannabis, then dosing patients on weed could make things worse, not better.

cannabis, medical cannabis, CBD, THC, recreational cannabis, hippocampus, brain regions, memory, seizures, research, memory loss

Image credit: Rainer Fuhrmann

Unfortunately, a lot of this research is still ongoing. If scientists are still sorting out how hippocampal volume affects seizures and depression, they know even less regarding cannabis’s long-term effects on brain structures.

Ethan Russo, a neurologist and cannabis expert based in Seattle, wrote to RxLeaf saying: “There is no definitive proof of permanent brain damage, hippocampal changes, or cognitive impairment in humans due to any level of cannabis usage that is not reversible after thirty days of abstinence.”

For eleven years, Russo worked as a pharmacological researcher at GW Pharmaceuticals. This is the company that developed cannabis-derived drugs like Sativex and Epidiolex. Epidiolex, used for treating difficult seizure disorders such as Dravet syndrome, is the first and only cannabis-derived pharmaceutical approved by the FDA in the U.S.. “There is minimal risk with cannabis-based medicines at customary lower doses required to treat symptoms of chronic diseases,” Russo added.

cannabis, medical cannabis, recreational cannabis, CBD, THC, depression, anxiety, seizures, hippocampus, memory, memory loss

Image credit: GW Pharmaceuticals

The Good News is CBD Protects The Hippocampus

The Cannabinoid Research study didn’t assess what kind of cannabis the subjects smoked, because that’s impossible. However, we can safely assume they smoked weed containing relatively high amounts of THC. Otherwise, why would they smoke it for years?

It’s possible that THC is what’s causing hippocampal shrinking. How do we know this? A study published in Translational Psychiatry (2016) looked at subjects who consumed cannabis with THC as well as cannabis with THC and CBD. Researchers then compared them to controls who reported either abstinence from cannabis for at least three months or never consuming cannabis at all.

cannabis, medical cannabis, recreational cannabis, CBD, THC, cannabinoids, seizures, depression, GW Pharmaceuticals, hippocampus, memory loss

Image credit: content_creator

The Translational Psychiatry study measured hippocampal structures through three methods. The first was MRI, like the Cannabinoid Research study mentioned above. The second was fractional anisotropy, another imaging technique that measures the connectivity within brain tissue (as opposed to just the volume, as was done in the first method).

The third method was N-acetyl aspartate (NAA) spectroscopic imaging. This measures the presence of the amino acid NAA in brain tissue. Amino acids are the building blocks of proteins, and proteins are the building blocks of tissues. Doctors and researchers commonly use NAA spectroscopic imaging to assess neuronal viability — the health of brain cells — since lower levels of NAA has links with neurodegeneration like that found in Alzheimer’s or other dementia patients.

What the Study Discovered

Anyway, what the Translational Psychiatry study found was fascinating: CBD appeared to protect the hippocampus from THC exposure. Subjects who only used high-THC cannabis had the most compromised hippocampi. Subjects who used CBD with THC had significantly less NAA and smaller volumes compared to controls. But they seemed better off than subjects who used THC alone. There were no differences in neural connectivity between the groups.

Regardless of whether subjects used only THC or CBD with THC, the hippocampus apparently returns to normal after cessation of cannabis consumption for twenty nine months. That doesn’t help seizure patients, since most of them will require cannabis therapies for the rest of their lives, but it does indicate that the brain possesses plasticity and that the hippocampus can regenerate.

cannabis, medical cannabis, recreational cannabis, CBD, THC, cannabinoids, hippocampus, memory loss, regeneration, seizures, depression

Image credit: Sanja Karin Music

So What Should We Do?

If you’ve ever witnessed someone undergo a grand mal seizure, then you know a little memory loss from cannabis oil is far more preferable than seeing them potentially die before your very eyes.

While THC may shrink the hippocampus, all the available data suggests there’s a limit to how much the hippocampus will shrink when exposed to THC. It’s not as if chronic cannabis consumption will disintegrate the hippocampus into oblivion, otherwise many of the people reading this would be legally brain-dead by now.

Every medication has side effects. Every medication carries risks. The goal in medicine is to minimize the serious harms caused by disorders and disease states, even if that goal comes with the smaller cost of a medication’s detrimental effects.

Which would you rather deal with? Permanent brain damage and possibly sudden death from a seizure, or forgetting where you put your car keys while you’ve got the munchies?


Randy Robinson

As someone who wanted to know everything but couldn't decide on anything, Randy completed degrees in English, World History, and Molecular Biology. During their studies, they received an externship at the biotech firm Cannabis Science Inc., focusing on phytocannabinoids as anti-tumor and anti-cancer agents. Based in the Mile High City of Denver, Colorado, you can find Randy on Twitter, Instagram, and Medium @RanDieselJay

1 Comment
  • Avatar
    Jenny Taylor

    Written with knowledge and great humor…

    June 3, 2019 at 1:26 am Reply

Post a Comment