What Causes Depression? Why Depression Is More Than a Chemical Imbalance

What Causes Depression Is a More Important Question Than It Sounds

What causes depression? That question sounds simple, but it may be one of the most important questions we ask in mental health care because depression describes what a person is experiencing more than it tells us why they are experiencing it. Two people can meet the same criteria for depression and have completely different causes underneath the symptoms. One person may be struggling because their thyroid is not working correctly. Another may have experienced a significant change in testosterone, estrogen, or progesterone. Another may be sleeping four hours a night, living in a destructive relationship, recovering from trauma, isolated from meaningful relationships, or gradually avoiding so many areas of life that confidence, accomplishment, connection, and hope have begun to disappear. Many patients have several of those things happening at the same time, which is why I often explain that depression is the symptom cluster, but the cause is the question.

This distinction matters because the treatment that makes sense depends heavily on what is actually causing the symptoms. If we identify the wrong cause, we can choose a perfectly reasonable treatment and still get disappointing results. A medication may help someone function while failing to address untreated thyroid disease. Therapy may provide support while missing severe sleep apnea. Hormone treatment may improve part of the picture while leaving an unhealthy relationship untouched. Good treatment begins by understanding the whole person well enough to know which of those possibilities actually applies.

Depression Is Not One Identical Illness in Every Person

People sometimes talk about depression as though everyone who receives the diagnosis has essentially the same condition. In reality, depression can look remarkably different from one person to another. One patient sleeps constantly while another cannot sleep. One overeats while another loses their appetite. One becomes emotionally numb while another feels overwhelmed by sadness. One feels physically exhausted while another becomes restless and agitated. Even though all of these people may meet the diagnostic criteria for depression, the pattern of symptoms can be dramatically different.

Researchers have demonstrated just how varied depression can be. A large analysis of patients in the STAR*D depression study found a tremendous number of different symptom combinations among people who all met criteria for major depression. Depression Is Not a Consistent Syndrome: An Investigation of Unique Symptom Patterns in the STAR*D Study That does not make the diagnosis useless. A diagnosis gives clinicians a common language, helps us recognize severity, and can guide treatment. But it should be the beginning of the investigation rather than a reason to stop asking questions.

Depression Is More Complicated Than a Chemical Imbalance

For many years, depression was commonly explained by telling patients that they had a “chemical imbalance,” often described as having too little serotonin. That explanation was easy to understand, but the science has never been that simple. A large systematic umbrella review examining the serotonin theory of depression found that the evidence does not support the simple idea that depression is caused by abnormally low serotonin levels or activity.

That does not mean antidepressants do not work, because antidepressants can be incredibly helpful for many patients. It means that the reason they help is more complicated than replacing a serotonin deficiency in the same way that insulin replaces insulin in someone with diabetes. Antidepressants affect brain signaling and neuronal functioning through several mechanisms, and for some patients those changes can dramatically improve mood, anxiety tolerance, sleep, motivation, and the ability to participate in therapy or make necessary changes in life.

This distinction becomes especially important when medication helps only partially or does not help at all. If a patient believes depression is simply a serotonin deficiency, they may understandably conclude that the only remaining question is which antidepressant they should try next. Sometimes that is the correct next step. Other times it means we need to step back and ask whether something else is continuing to drive the depression.

Medical Problems Can Look Exactly Like Depression

One of the most important lessons I learned as a psychiatrist is that the body can produce symptoms that look completely psychiatric. I have treated patients whose low energy, weight gain, lack of motivation, cognitive slowing, and depressed mood looked like ordinary depression until a broader medical evaluation showed that their thyroid was the real problem. Once the thyroid disorder was treated appropriately, the symptoms that had been labeled depression improved because we had finally treated the actual cause.

Hormones can create a very similar picture. A man whose testosterone has declined may experience low motivation, fatigue, brain fog, weight gain, reduced strength, decreased sexual desire, and depressed mood. A woman moving through perimenopause may suddenly experience poor sleep, night sweats, brain fog, emotional volatility, anxiety, loss of sexual desire, and depressive symptoms even though nothing obvious has changed psychologically. The postpartum period gives us another powerful example because a new mother may simultaneously be dealing with dramatic hormonal changes, physical recovery from childbirth, fragmented sleep, breastfeeding demands, relationship changes, loss of independence, anxiety, and the enormous responsibility of caring for a newborn.

This is why a good depression evaluation sometimes needs to look beyond traditional psychiatry. Depending on the symptom pattern, that may mean considering thyroid evaluation, testosterone replacement therapy, women’s hormone treatment, postpartum care, sleep problems, medication side effects, nutrition, metabolic health, or a broader comprehensive wellness evaluation. It does not mean every patient with depression needs every test. It means the story should determine which questions deserve to be asked.

Psychological Causes of Depression Are Just as Real

Recognizing medical causes does not mean every depression is caused by a laboratory abnormality. Psychological, relational, and environmental experiences can profoundly affect mental health. A person may become depressed after betrayal, grief, chronic criticism, trauma, loneliness, repeated failure, prolonged stress, loss of an important relationship, or years of feeling unheard, unseen, or unappreciated. Sometimes the cause is obvious, but other times the person has lived inside the pattern for so long that they no longer recognize how much it is affecting them.

This is one reason good therapy should eventually go deeper than simply giving someone a comfortable place to talk about the week. The therapist should help the patient understand which patterns are contributing to the depression, what is maintaining those patterns, what needs to change, and what makes those changes difficult. Some of those causes will be conscious, while others may not be. A patient may know their marriage is failing but not understand the repeated behavior pattern that keeps creating conflict. Another may know work makes them miserable while never recognizing how consistently they have avoided the steps necessary to change their professional situation. Another may feel profoundly lonely despite being surrounded by people because none of those relationships provide genuine emotional connection.

Avoidance Can Quietly Make Depression Worse

One of the patterns I discuss extensively in Start is what happens when people repeatedly move away from things that are difficult. Avoidance usually works very well in the short term. If a difficult conversation makes you uncomfortable, avoiding it reduces the discomfort. If applying for a better job makes you feel inadequate, not applying brings immediate relief. If social interaction creates anxiety, staying home can feel safer. If vulnerability in a relationship creates fear of rejection, emotional distance may temporarily protect you from being hurt.

The problem is that avoidance usually fixes the discomfort without fixing the problem. The difficult conversation remains unresolved. The better job is never pursued. Social confidence decreases. The relationship becomes more distant. Responsibilities accumulate. The next attempt feels even harder because the person has fewer experiences proving that they can successfully handle the situation. Over time, a person's world becomes smaller while the things they are avoiding become larger.

This is part of what I describe in Start as the Adversity Cycle. When people consistently avoid what is difficult, they lose opportunities to build the skills and confidence that would make those situations easier in the future. Anxiety rises because normal challenges begin to feel increasingly overwhelming, and discouragement can eventually become depression because the future starts to feel stagnant, limited, or hopeless. This pattern does not explain every case of depression, but I have seen it play a major role in many patients whose symptoms initially seemed mysterious.

Depression Often Involves the Loss of Meaningful Accomplishment

Human beings need more than comfort. One of the central ideas in Start is that people tend to function best when they experience both meaningful accomplishment and healthy social connection. Accomplishment does not mean becoming wealthy, famous, or professionally impressive. It means engaging with life in ways that build capability, contribution, progress, and the sense that your effort is moving you toward something that matters.

This helps explain why someone can have a relatively comfortable life and still become depressed. If every difficult responsibility has gradually been removed, the person may experience less immediate stress while simultaneously losing the sense that they are growing or accomplishing anything meaningful. Life may become easier while also becoming increasingly empty. The opposite can happen as well: someone can be under tremendous stress and still remain emotionally strong when that stress is connected to a meaningful purpose.

I experienced this personally during my military service. Some of the most stressful periods of my life occurred while working in environments where the stakes were extremely high, yet the work mattered deeply and I knew why I was doing it. In other periods, comparatively comfortable responsibilities that felt meaningless were far more emotionally draining. The difficulty itself was not the only thing that mattered. Whether the difficulty was connected to something meaningful mattered enormously. This does not mean someone can cure severe depression by simply becoming busier. Meaningless busyness can make things worse. It means that progress toward something genuinely important can change how life feels.

Healthy Social Connection Matters Too

Meaningful accomplishment by itself is not enough because people also need healthy social connection. A person can be professionally successful, financially secure, and highly accomplished while still becoming profoundly depressed if they are emotionally isolated. Healthy connection is more than simply having people nearby. It means having relationships where we feel heard, seen, appreciated, valued, and capable of being known by the people who matter to us.

This is why loneliness can exist inside a marriage, inside a family, inside a workplace, or inside a large social group. The problem is not always the number of people around us. Sometimes the problem is that none of those relationships are deep or safe enough to create genuine connection. Healthy connection also does not mean surrounding ourselves only with people who make us comfortable. Some of the healthiest relationships in our lives involve people who care enough to challenge us, expect growth, tell us difficult truths, and remain connected while we learn.

Later in this series, we will spend an entire article on accomplishment and social connection because these two factors are often overlooked when depression treatment focuses only on symptom reduction. A person may need medication or therapy and still need to rebuild a life where they are accomplishing things that matter and connecting meaningfully with other people.

Depression Can Grow When Several Areas of Life Collapse at Once

Another framework from Start is to look at life across five broad areas: professional life, romantic relationships, family relationships, social life and hobbies, and spiritual or ethical growth. People do not need perfect balance across all five because real life does not work that way. There will be seasons when parenting requires unusual attention, professional development temporarily demands more time, or health becomes the priority.

The problem occurs when important parts of life are abandoned for long periods of time. Someone may be doing wonderfully at work but have no meaningful romantic or family connection. Another may be socially active and surrounded by friends but have no sense of professional progress, discipline, or responsibility. Another may be devoted to family while having lost every hobby, friendship, personal goal, or area of growth that once gave them an individual identity.

When several areas deteriorate at the same time, people can begin feeling as though their entire life is failing even when one or two areas still look successful from the outside. This is why depression treatment sometimes requires asking a much larger question than, “How sad have you been this week?” The more useful question may be, “What has changed in your life that has reduced your ability to feel successful, connected, capable, purposeful, or hopeful?”

Trauma and Chronic Threat Can Contribute to Depression

Trauma can also contribute to depression, particularly when a person's threat system remains activated for long periods of time. In Conquering PTSD, I explain that the emotional center of the brain is constantly looking for potential danger and that anxiety is one of the ways it communicates that something needs to be analyzed. When that system remains chronically “on call,” it becomes much harder to relax, connect with other people, sleep normally, focus, enjoy hobbies, experience intimacy, or simply feel safe enough to enjoy life.

A person in that state may describe anxiety as the most obvious symptom, but depression can gradually develop alongside it. If someone spends months or years feeling unsafe, avoiding people and places, sleeping poorly, losing activities they once enjoyed, and becoming increasingly isolated, it should not surprise us when hopelessness and depressive symptoms eventually appear. This is one reason depression and anxiety so commonly travel together, and later in this series we will devote an entire article to explaining how those two patterns reinforce one another.

Sometimes Depression Has More Than One Cause

Real patients rarely fit perfectly into one box. A woman may be moving through perimenopause while also dealing with a difficult marriage and chronic sleep deprivation. A man may have declining testosterone while simultaneously feeling disconnected from his children and professionally stagnant. A person with PTSD may also have untreated sleep apnea, medication side effects, and a shrinking social life. Trying to force those patients into a choice between a “biological cause” and a “psychological cause” misunderstands how people actually work.

Often the answer is both. The brain, body, relationships, environment, habits, unconscious patterns, sleep, hormones, and life experiences are interacting all the time. This is why I become uncomfortable when anyone wants to explain every depression with one theory. Human beings are far too complicated for that, and treatment should be broad enough to recognize that several contributors may need to be addressed at the same time.

If Depression Has a Cause, Why Do Antidepressants Help?

If depression is not simply a serotonin deficiency, an obvious question follows: why can an antidepressant still make someone feel dramatically better? The answer is that a treatment does not have to correct the original cause in order to help a struggling system function better while healing takes place. Antidepressants affect brain signaling in ways that are much more complex than simply “adding serotonin,” and for many patients those changes improve mood regulation, anxiety tolerance, sleep, motivation, emotional stability, and the ability to participate in therapy or make necessary changes.

At Dynamic Psychiatry & Wellness, we do not view psychiatric medication management and root-cause treatment as competing philosophies. Medication may be exactly what gives someone enough stability to begin confronting trauma, repairing a marriage, returning to work, rebuilding social connection, exercising, sleeping better, or making the changes that eventually reduce the factors contributing to depression. The important point is that improvement with medication does not prove that the depression was originally caused by a medication deficiency. Medication is a tool, and we still want to understand the person who needs that tool.

Depression Treatment Should Match the Cause

Once we stop assuming every depression is identical, treatment becomes much more logical. Someone with a major thyroid problem needs thyroid treatment. Someone whose depression is being driven heavily by trauma may need trauma-focused psychotherapy. Someone with severe biological depression may benefit substantially from antidepressant medication. Someone who has not improved enough with medication may be a candidate for TMS or ketamine-assisted therapy. Someone whose life has gradually collapsed through avoidance may need therapy that helps them begin engaging with difficult areas again, while someone whose strongest problem is profound loneliness may need to rebuild meaningful relationships rather than simply adding another medication.

Many patients need several of those things together, and that is why the goal is not to prove that medication is always the answer, therapy is always the answer, or hormones, sleep, TMS, ketamine, relationships, exercise, or lifestyle are always the answer. The goal is to understand why this particular person is depressed and then choose the tools that fit the actual causes that are present.

When Depression Becomes Dangerous

Depression deserves serious attention because it can progress from discouragement and withdrawal into profound hopelessness and suicidal thinking. A person should not have to wait until they are completely unable to function before seeking help. Worsening isolation, inability to work or care for responsibilities, major changes in sleep or appetite, increasing substance use, overwhelming hopelessness, or thoughts that life is no longer worth living are all signs that professional support is needed.

If someone is thinking about suicide, believes they may harm themselves, or cannot remain safe, treatment should become urgent rather than waiting for the perfect explanation of why the depression developed. In the United States, the 988 Suicide & Crisis Lifeline is available by calling or texting 988, and emergency services should be used when there is immediate danger. Protecting the person comes first; once immediate safety is established, the deeper work of understanding what is driving the depression can continue.

The Goal Is Not Just to Reduce Depression

Reducing symptoms matters because someone who cannot sleep, think clearly, get out of bed, experience joy, or function in everyday life deserves relief as quickly as we can safely provide it. But long-term recovery requires more than reducing a score on a depression questionnaire. We want to understand what changed, what is maintaining the symptoms, and which medical, psychological, relational, behavioral, and lifestyle factors apply to that individual.

From there, the goal is to help the person regain the ability to work, connect, love, think, grow, accomplish meaningful things, and participate fully in life. That is why the question “What causes depression?” matters so much. Depression should not be treated as nothing more than a label attached to someone who feels terrible. It is a signal that something in the person's mental, physical, relational, emotional, or behavioral world is not functioning the way it should.

The diagnosis tells us what they are experiencing. Good treatment asks why.