Why I See Depression As A Symptom — Not A Diagnosis
People are always surprised when they hear me—a psychiatrist for more than 40 years—say that I don't like the diagnosis of depression.
Why do I say that? Imagine if you had crushing chest pain and you went to see your cardiologist and they simply gave you a diagnosis of chest pain. The problem is that it doesn't tell you what's causing your symptoms or what to do about it. With depression, it's the same thing.
Being diagnosed with depression doesn't indicate the root cause of your depressive symptoms, and it doesn't help target treatment. It's part of the reason treatment-resistant depression is so common. One randomized controlled trial1 found that over half of depressed people don't experience relief from symptoms when treated with antidepressants. Even worse, about one in three individuals with depression fail to achieve remission following four courses of antidepressant treatment.
Treatment failures are far too common, in large part because depression isn't a single or simple disorder. There are many possible causes of depression. Some of the most common biological factors that I see contribute to depression include:
Low thyroid levels
An underactive thyroid can make you feel sluggish, and decades of research show that it is linked to depression. According to a 2022 review, hypothyroidism is one of the primary underlying causes of treatment-resistant depression2. Low thyroid also impacts brain function.
At Amen Clinics, we use a brain imaging technology called SPECT to look at the brains of our patients. SPECT measures blood flow and activity. On brain SPECT scans, low thyroid levels are associated with overall low activity in the brain, which we also see in patients with brain fog and depression.
Exposure to mold
Living in a moldy home or working in an office where mold is present can dampen your mood. Research from Brown University involving nearly 6,000 people found a strong connection between mold and depression.
Growing up, my best friend was my grandfather, who was always smiling and happy. He was a candy-maker, and some of my best memories are of making fudge with him. But all that candy took a toll, and at age 69, he had a heart attack. After that, everything changed. He cried a lot, seemed unhappy, couldn't sleep, and was eventually diagnosed with depression. I didn't know it at the time, but depression is three times more common in people following a heart attack, according to research.
Mild traumatic brain injuries—even ones that don't cause you to black out or don't get diagnosed as a concussion—can change your life in so many ways. Depression is just one of them. According to a 2020 study in Frontiers in Neurology, people with a history of a mild head injury are over three times as likely to have depression3 compared with individuals who have not experienced head trauma.
In about 40% of our patients at Amen Clinics, the brain scans show evidence of previous head trauma.
In about 40% of our patients at Amen Clinics, the brain scans show evidence of previous head trauma. Surprisingly, many of those patients either don't remember getting injured or think their injury was so minor it wasn't worth mentioning. They would never make the connection between their current depressive symptoms and falling off a bike as a kid or getting in a fender bender as a teen.
Infections are a major cause of psychiatric disorders, such as depression, but few people know it. In particular, a significant number of people are experiencing depressive symptoms post-COVID. A 2021 study in JAMA Network Open found that 52.4% of post-COVID patients met the criteria for major depressive disorder4 several months after being infected.
The brain imaging work at Amen Clinics shows that having COVID is associated with increased activity in the limbic system (emotional centers) of the brain. This is a common brain activity pattern also seen in people with depression.
It's clear that depression can be a complex disorder with multiple causes. That's why it's so important to undergo comprehensive testing to determine the root cause or causes of your depression. Only by addressing all of the underlying causes can you truly heal from this potentially debilitating condition so you can start feeling happier and more positive.
Daniel Amen, MD, is a clinical neuroscientist psychiatrist, physician, professor and 10-time New York Times bestselling author. He is a double board-certified child and adult psychiatrist and founder of Amen Clinics, Inc., which has eight clinics across the country with one of the highest published success rates for treating complex psychiatric issues with the world’s largest database of functional brain scans relating to behavior, with more than 160,000 scans on patients from 121 countries. Amen is the lead researcher for the largest brain imaging and rehabilitation study for professional football players that demonstrates high levels of brain damage in players with solutions for significant recovery as a result of his extensive work. His research on post-traumatic stress disorder and traumatic brain injury was recognized by Discover magazine’s Year in Science issue as one of the “100 Top Stories of 2015.” Amen has authored and co-authored more than 70 professional articles, seven scientific book chapters and 40-plus books, including the No. 1 New York Times bestsellers, “The Daniel Plan” and “Change Your Brain, Change Your Life.” His most recent book, “Change Your Brain, Change Your Grades,” includes editorial contributions from his teenage daughter, Chloe Amen, and niece, Alizé Castellanos.