It's not that unusual for a patient to try one antidepressant, then another, then a third. Doses are adjusted, medications layered, side effects accumulate and, still, the symptoms persist. Eventually, the patient's condition may be labeled treatment-resistant depression. For many, that's where the search stops. But a new study suggests that for some people with depression, it may be exactly where the search should begin.

The research team followed over 8,100 patients seen in clinical practices in Philadelphia, Memphis and New York City, over six years. All had documented dysfunction of the autonomic nervous system, which quietly regulates heart rate, blood pressure, digestion and blood flow to the brain. Some had had long COVID.

Nearly 2,200 of these patients had been previously diagnosed with depression or depression-like symptoms. The patients were, on average, about 50 years old, and nearly 58 percent were women.

“What we found, again and again, was that these [depressed] patients were not treatment resistant in any meaningful psychiatric sense. Their brains were being starved of blood.”

What set this group apart wasn't just their diagnoses; it was the complexity of their symptoms.

These patients reported, on average, 23 out of 28 possible autonomic symptoms, including crushing fatigue, brain fog, dizziness on standing, poor sleep, memory lapses, chronic pain, gastrointestinal issues and heightened sensitivity to light and sound.

The point wasn't to catalogue these symptoms. The researchers were asking a different question: What if in some cases depression isn't the result of brain chemistry, but instead, of blood flow?

To answer that, the team used a specialized technique called parasympathetic and sympathetic (P&S) monitoring. Unlike standard methods, which estimate nervous system activity indirectly, this approach separates responses from the two branches of the autonomic system — "fight or flight” and “rest and digest” — by incorporating signals alongside heart rate variability.

This distinction matters. Without it, clinicians can misread whether the body is overactive, underactive or simply compensating.

Their finding was important. In nearly 80 percent of those with depression in this group, there was alpha sympathetic withdrawal, the term for a condition where blood pools in the lower body when a person sits or stands, limiting circulation to the brain. More than half also had parasympathetic excess, meaning blood vessels relaxed when they should have remained constricted, further reducing effective blood flow.

The result? The brain, arguably the body's most energy-demanding organ, wasn't getting what it needed.

“What we found, again and again, was that these patients were not treatment resistant in any meaningful psychiatric sense. Their brains were being starved of blood,” corresponding author Dr. Joe Colombo of the Franklin Cardiovascular, Autonomic Dysfunction and POTS Center in New Jersey, explained in a press release.

If symptoms like fatigue, dizziness, brain fog and poor sleep accompany depression, especially after illness or prolonged stress, it may be worth asking whether the body, not just the mind, needs attention.

That reframing changed everything. Instead of escalating psychiatric medications, the researchers treated the underlying physiology. Their approach was deliberately “low and slow,” using low-dose medications to correct specific autonomic imbalances.

For patients unable to tolerate drugs, alternatives included R-alpha-lipoic acid to support nerve function and a carefully structured walking program which was no faster than two miles per hour — a rate originally designed for astronauts returning from space. The goal wasn't to override the system, but to retrain it.

The results were encouraging. Within three months, many patients reported improved sleep. Over six to nine months, symptoms like fatigue and brain fog began to ease. By the end of treatment, which typically lasted between 9 to 12 months, the average number of symptoms dropped dramatically, from 23.2 to 5.2. Fatigue improved in over 77 percent of patients and a third finished with three or fewer symptoms remaining.

Importantly, nearly half the participants had long COVID, a condition linked to autoimmune dysfunction. Others had hypertension, diabetes or orthostatic issues. These are conditions often treated separately, but here were revealed to be interconnected through their effects on circulation and nervous system balance.

For patients, the takeaway is not to abandon psychiatric care, but to broaden the lens. If symptoms like fatigue, dizziness, brain fog and poor sleep accompany depression, especially after illness or prolonged stress, it may be worth asking whether the body, not just the mind, needs attention.

Sometimes what looks like a mental health impasse is actually a physiological bottleneck, one that, once recognized, can begin to open. As this research shows, depression's roots may be more physical than we thought.

The study is published in Brain Medicine.