A new study claims cannabis use may cause accelerated brain aging, but experts say the findings appear to “prioritize marketing over science.”

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Can cannabis use cause accelerated brain aging? Illustration by Ruth Basagoitia

A new study has identified cannabis, alcohol, and certain mental disorders as primary drivers of brain aging.

Billed as the largest known brain imaging study, utilizing more than 60,000 SPECT scans, the research looks impressive.

It also supports an enticing prospect: being able to look at images of the brain to see whether or not it’s prematurely aging.

But experts have called the research into question over the methodology, which has a long history of criticism among members of the medical community.

The research was conducted by Dr. Daniel Amen, a psychiatrist who runs Amen Clinics which specializes in SPECT (single photon emission computed tomography), as well as scientists from Google, UCLA, and Johns Hopkins University.

In total, the team analyzed 62,454 SPECT scans of more than 30,000 patients ranging in age from under 1 year to 105 years old. The scans used for the study were all drawn from patients at Amen’s clinics.

“Based on one of the largest brain imaging studies ever done, we can now track common disorders and behaviors that prematurely age the brain. Better treatment of these disorders can slow or even halt the process of brain aging,” said lead author Daniel Amen.

On the surface, the concept of the study appears straightforward: like other parts of the human body, stress and strain can accelerate the aging process.

For an athlete this could show up in shoulders or knees because of years of physical activity. For someone with a history of heavy alcohol use it could be the liver.

The idea is that, at a given age, your body and organs should look and function a certain way and the brain is no different.

The effects of different conditions on the brain — such as substance use or mental disorders — can cause brains to age prematurely, resulting in lower cognitive function, declining memory, and an increased risk of Alzheimer’s disease and dementia.

Using SPECT imaging technology and looking at blood perfusion (blood flow) in the brain, the researchers compared what they saw to the actual chronological age of the brain and established a “brain estimated age,” — how much the brain appeared to have aged.

Blood perfusion in the brain is known to change over time, and the researchers contend that using it as a biomarker could “powerfully predict chronological age and will vary as a function of common psychiatric brain disorders.”

The conditions they studied as drivers of brain aging included dementia, ADHD, major depression, bipolar disorder, generalized anxiety disorder, traumatic brain injury, schizophrenia, alcohol use disorder, and cannabis use disorder.

Of these conditions, schizophrenia contributed to brain aging the most with an average of four years of premature aging, followed by cannabis abuse (2.8 years), bipolar disorder (1.6 years), ADHD (1.4 years), and alcohol abuse (0.6 years).

Part of what has brought attention to the study is the simple fact that cannabis use sits so high on that list.

“People sort of think of it as an innocuous drug, but that’s not what our studies or our experience is telling us,” Amen told Healthline. “The evidence I have from the world’s largest imaging database and experience over the last nearly 40 years is that it harms the brain. It decreases blood flow to the brain, it makes your brain more toxic.”

However, that assertion, like others in the study, has come under fire.

The scientific literature on marijuana and Alzheimer’s is by no means clear cut.

Some studies have identified both THC and CBD — two of the many chemical components found within marijuana — as having potentially beneficial effects on Alzheimer’s and dementia.

Advocates disagree with how the drug is being characterized by Amen.

“There is some exciting preliminary data, based largely on animal models, that components in cannabis can be neuroprotective and may possibly hold keys to addressing the aging process in the brain and/or age-related disorders,” Paul Armentano, the deputy director of the National Organization for the Reform of Marijuana Laws (NORML), told Healthline.

“Obviously, these findings and their implications appear to be opposite of those suggested by Dr. Amen,” Armentano said.

Amen’s findings concerning the impact of marijuana use on brain aging may have been the most visible issue stemming from the study, but it’s hardly the only bone others have had to pick with him and his work.

To say that Amen has a notorious reputation within the medical community would be an understatement.

He’s been called a fraud, a snake oil salesman, and a huckster.

One expert at UCLA’s Brain Research Institute contacted by Healthline said “I have nothing to add beyond what has already been said by others,” and suggested he should be investigated by the medical board.

He declined to comment further.

The issue that many take with Amen is his use of SPECT. The technology itself is nothing new — it’s been around for about three decades.

It uses radioactive tracers injected into the blood, which can be used to measure blood flow in the organs of the body or help detect and diagnose coronary artery disease or abnormalities in the brain.

Amen’s work uses SPECT to look at blood perfusion and activity in the brain to assist in identifying and diagnosing mental disorders, a contentious practice that’s frowned upon by his peers.

“Psychiatrists are the only medical doctors who virtually never look at the organ that they treat,” said Amen. He makes the intuitive argument that biomarkers and functional brain imaging should be used in psychiatry.

That theory isn’t supported by many outside of a minority of mental health practitioners.

In 2012, the American Psychiatric Association issued a consensus report on the use of neuroimaging for psychiatric disorders and stated, “currently neuroimaging is not recommended within either the U.S. or the European practice guidelines for positively defining diagnosis of any primary psychiatric disorder.”

Seth J. Gillihan, PhD, a clinical psychologist and clinical assistant professor of psychology in the Department of Psychiatry at the University of Pennsylvania, has published on the topic of Amen’s work and how it’s situated within these guidelines.

He says that using brain imaging diagnostically is definitely plausible because of the way some mental illnesses have identifiable biological markers, but the problems preventing its implementation are manifold.

Regarding Amen’s new study: its finding are exciting — if in fact they’re true.

“There may be multiple things that affect blood flow to the brain and we shouldn’t necessarily conclude that just because something has the same correlation with blood flow to the brain that age does, that therefore that condition is causing age-related changes in the brain,” he told Healthline.

For those looking in from the outside, Amen’s work can appear baffling and pseudoscientific.

But Amen argues that others in his field don’t share the same level of expertise that he and his team do from years and years and thousands of scans using SPECT technology.

“We have a database of 150,000 scans on patients from 120 countries. When we see a scan we really have a good sense of what it means,” he told Healthline.

For many, including Gillihan, that assertion isn’t enough to justify the claims made by Amen in his research.

It’s an attractive prospect to ascertain specific knowledge on mental health conditions, but experts say the technology just isn’t capable of doing this — yet.

As for the specific claims of this study?

“The researchers seem to have ignored or dismissed obvious alternative explanations for their findings, focusing their discussion instead on promoting the usefulness of SPECT scans for determining a person’s ‘Brain Estimated Age.’ As such, this study appears to prioritize marketing over science,” said Gillihan.