Depression has been recognized as a distinct condition for at least 2,400 years, though what people called it, what they blamed it on, and how they tried to treat it changed dramatically from one era to the next. The story moves from ancient Greek physicians who believed a literal black fluid pooled in the body, through centuries of religious explanation, to the accidental discovery of the first antidepressants in the 1950s and the diagnostic systems still in use today.
Ancient Greece and Black Bile
The Greek physician Hippocrates, working around 400 BCE, is often credited with the theory of the four humors: blood, yellow bile, black bile, and phlegm. Each fluid supposedly governed a person’s temperament, and an imbalance in any direction produced illness. Depression, or what the Greeks called melancholia, was tied specifically to an excess of black bile. The word itself reflects this belief: “melas” (black) and “kholé” (bile).
This wasn’t just a metaphor. Greek and later Roman physicians treated melancholia as a medical condition with physical roots, prescribing dietary changes, exercise, bathing, and herbal remedies to restore humoral balance. The framework persisted for well over a thousand years. Even in Shakespeare’s era, “melancholy” remained the most complex of emotional states, and aging was thought to produce an excess of the dark humor, explaining the sadness and irritability associated with old age.
The Middle Ages: Sin, Demons, and Acedia
During the medieval period, explanations for persistent low mood shifted heavily toward the spiritual. Belief in demonic possession became a widely accepted explanation for erratic or disturbed behavior across Western Europe. If mental illness resulted from possession by demons, the logical treatment was to expel those demons through prayer, rituals, or exorcism. Monasteries also recognized a state called “acedia,” a profound listlessness and spiritual despair that afflicted monks, sometimes described as the “noonday demon.” It looked a great deal like what we would now call depression, but it was understood as a failure of faith rather than a medical problem.
Humoral medicine didn’t vanish entirely during this period. It coexisted uneasily with religious explanations, and some physicians continued to treat melancholia with herbs and physical remedies. But the dominant cultural framework placed the soul, not the body, at the center of mental suffering.
Robert Burton and the Anatomy of Melancholy
In 1621, the English scholar Robert Burton published “The Anatomy of Melancholy,” one of the most influential texts ever written about depression. Running to nearly 1,400 pages across multiple editions, it attempted to catalog every possible cause and cure for the condition. What made Burton unusual for his time was that he bridged two frameworks. He accepted the inherited humoral theory descending from the ancient physician Galen, but he also observed something that wouldn’t be formally studied for another 350 years: that the loss of loved ones, social status, or personal health frequently preceded episodes of melancholy.
Burton, more clearly than other seventeenth-century writers, identified traumatic loss as a trigger for mood disorders. His “etiological hunches,” as one modern psychiatric review put it, have found verification in recent research on grief, trauma, and depression. The book also treated melancholy as a universal human experience rather than a rare affliction, an idea that was ahead of its time.
Kraepelin and the Birth of Psychiatric Classification
The late 1800s brought a fundamentally different approach. The German psychiatrist Emil Kraepelin set out to classify all mental illness the way other branches of medicine classified physical disease. His most consequential move was dividing the major psychoses into two categories: “dementia praecox” (now called schizophrenia) and “manic-depressive insanity” (the ancestor of modern bipolar disorder and major depression).
Kraepelin’s concept of manic-depressive insanity was far broader than today’s bipolar disorder. It included single episodes of depression with no mania, circular patterns of highs and lows, mild chronic mood disturbances, and states of profound confusion. In his view, all of these were expressions of a single underlying disease process, separated only by degree. He wrote that all these forms “pass over the one into the other without recognizable boundaries” and could even replace each other within the same patient over a lifetime. This was the first systematic attempt to treat depression as a classifiable medical entity rather than a philosophical or spiritual condition.
The Accidental Discovery of Antidepressants
The first effective drug treatments for depression were discovered entirely by accident in the 1950s. Chemists at the pharmaceutical company Hoffmann-La Roche had developed iproniazid as a treatment for tuberculosis. It worked against TB, but clinicians noticed striking “side effects” in their patients: euphoria, increased appetite, improved sleep, and a general psychic brightening. In 1958, a systematic study gave iproniazid to patients with depression for several weeks and reported significant improvements in 70% of them. Though it was marketed as a tuberculosis drug under the trade name Marsilid, physicians began prescribing it off-label for depression. It became the first successful pharmacological treatment for the condition and the founding member of a drug class called MAO inhibitors.
The second accidental discovery came from the search for better antipsychotic drugs. A compound called imipramine had been synthesized by modifying the structure of an antihistamine, and it was given to the Swiss psychiatrist Roland Kuhn to test in patients with schizophrenia. It did nothing for psychosis, but Kuhn noticed dramatic improvements in patients who were severely depressed. In a 1958 essay, he described the transformation: patients resumed activities, sought out other people, began to laugh again, and reported that the heaviness in their limbs and the oppression in their chests had lifted. Imipramine became the first tricyclic antidepressant and opened an entirely new chapter in treatment.
The Serotonin Hypothesis
These accidental drug discoveries created a puzzle: the medications worked, but nobody understood why. In 1965, Joseph Schildkraut proposed what became known as the monoamine hypothesis of depression, suggesting that the illness originated from a deficit in certain brain chemicals called catecholamines (a family that includes norepinephrine and dopamine). Two years later, Alec Coppen shifted emphasis to serotonin, arguing that low levels of this particular chemical messenger were central to depression.
This “chemical imbalance” theory became the dominant explanation for depression for decades. It was elegant and intuitive: depression was caused by too little serotonin in the brain, and antidepressants corrected the shortfall. The reality turned out to be far more complicated. Antidepressants raise serotonin levels within hours, but symptom relief takes weeks, suggesting the drugs work through slower, more complex biological pathways. Still, the serotonin hypothesis drove drug development for the rest of the twentieth century and shaped how millions of people understood their own illness.
Prozac and the SSRI Era
On December 29, 1987, the FDA approved fluoxetine, manufactured by Eli Lilly under the trade name Prozac, for the treatment of major depressive disorder. It was the first of a new class of drugs called selective serotonin reuptake inhibitors, or SSRIs. These drugs targeted serotonin more precisely than the older medications, which meant fewer side effects and a wider margin of safety in overdose.
Prozac became a cultural phenomenon in a way no psychiatric medication had before. It appeared on magazine covers, inspired bestselling books, and reshaped public conversation about depression. For the first time, millions of people who might previously have suffered in silence had a treatment that was relatively easy to take and that their general practitioners, not just psychiatrists, could prescribe. The SSRI era didn’t just change pharmacology. It changed the social acceptability of admitting to depression and seeking help for it.
How the Diagnosis Itself Evolved
The way clinicians formally define depression has gone through its own transformation. The first Diagnostic and Statistical Manual (DSM), published in 1952, reflected the psychodynamic thinking of the era. Depression was classified as a “depressive reaction,” a term that implied the condition was fundamentally a psychological reaction to life stressors, rooted in Freudian ideas about unconscious conflict. The second edition in 1968 dropped the word “reaction” but kept the same psychodynamic framework largely intact.
The real break came with DSM-III in 1980, which replaced psychodynamic formulations with symptom-based checklists that were deliberately agnostic about what caused the illness. For the first time, two clinicians evaluating the same patient could use the same standardized criteria and arrive at the same diagnosis. This shift toward reliability over theory made large-scale research possible and established the template that DSM-IV (1994) and DSM-5 (2013) refined. The definition of major depressive disorder that clinicians use today, built around specific symptoms lasting at least two weeks, descends directly from this 1980 overhaul.
Electrical Treatments and Physical Interventions
Alongside drug therapy, physical treatments for depression followed their own path. The roots of electroconvulsive therapy trace to 1934, when the Hungarian physician Ladislas Meduna theorized that induced seizures might treat psychiatric illness. He injected an epilepsy-causing agent into a mute, catatonic patient and triggered a generalized seizure. The approach showed promise, but patients endured minutes of terror and severe physical stress while waiting for the seizure to begin.
An Italian team led by Ugo Cerletti and Lucio Bini refined the method by using electrical current applied to the skull, which produced seizures almost instantly. Over the following decades, the procedure became progressively less harrowing. In 1944, shorter electrical pulses reduced confusion and cognitive side effects. By 1952, the introduction of general anesthesia during the procedure made it far more tolerable. Modern electroconvulsive therapy bears little resemblance to its early versions and remains one of the most effective treatments for severe depression that doesn’t respond to medication.
The history of depression is, in many ways, a history of people reaching for whatever framework their era offered to explain a universal form of suffering. Black bile gave way to demonic possession, which gave way to unconscious conflict, which gave way to chemical imbalances, which is now giving way to more nuanced models involving neural circuits, inflammation, genetics, and life experience. Each era believed it had found the answer. Each turned out to hold only part of it.