People say "depressed" about a bad week and about a state that flattens a life for months. Major depressive disorder describes the second case: a set of lasting symptoms affecting mood, but also sleep, energy, appetite and thinking. It is neither a character trait nor a lack of willpower, its course varies widely from one person to another, and effective treatments exist.
What the diagnosis covers
The diagnosis is about an episode, not a hard day. It requires that, nearly every day for at least two weeks, there is low mood or a loss of interest and pleasure, at minimum one of the two. Several other changes come with it: disrupted sleep in either direction, fatigue, altered appetite and weight, slowing down or agitation, trouble concentrating and deciding, a sense of worthlessness or excessive guilt, thoughts turning towards death.
Two conditions are often forgotten. The symptoms have to affect real life. And other causes must be ruled out, in particular a physical illness such as a thyroid problem, a medication being taken, or substance use. That is why a diagnosis is not made by filling in a questionnaire alone in front of a screen.
Anhedonia, the loss of the capacity to feel pleasure, is often more telling than sadness itself. Many people describe less a grief than an anaesthesia: nothing hurts much, but nothing appeals either.
Sadness, character, willpower
Depression is not intense sadness. Grief is reactive: it moves with events and lets moments of relief through. An episode settles in more continuously, often without a cause proportionate to it, and touches functions that have nothing to do with mood, such as sleep, working memory or the perception of physical pain.
It is not a personality trait. Someone in an episode can look pessimistic, slow or closed off when those traits did not describe them before and will not describe them afterwards. Mistaking the state for the person is one of the main sources of misunderstanding among those close by.
It is not a lack of willpower. Telling someone to snap out of it runs into a simple fact: loss of drive is a symptom, not a refusal to get better. Asking for more willpower treats the symptom as though it were the cause.
Then there is bereavement. Losing someone causes deep pain that is not in itself an illness, but grief can come with a depressive episode. The difference shows in how the pain evolves and in whether self-worth stays damaged, not in how intense the sorrow is.
Presentations that look nothing alike
The classic picture, someone switched off and motionless, is far from the only one. In some people an episode shows up mainly as irritability, constant edginess, intolerance of noise and of anything unplanned. In others it speaks first through the body: diffuse pain, digestive trouble, unexplained exhaustion. Those presentations go unrecognised longest, precisely because they do not match the expected image. Age shifts the picture too: in adolescents, irritability and withdrawal from school often dominate; in older adults, memory complaints can be taken for cognitive decline when they belong to the episode.
Major depressive disorder is also distinct from persistent depressive disorder, formerly called dysthymia, which describes chronically low mood rather than bounded episodes. Some people have both.
One distinction matters more than the rest: bipolar disorder. A depressive episode can be the first visible sign of a bipolar condition whose high phases, hypomania especially, go unnoticed or are remembered as good stretches. That is why a clinician asks about the whole history: the direction of treatment depends on it.
What is established and what is debated
The agreement is that depression is multifactorial. A partly inherited vulnerability, difficult life events, prolonged isolation, some chronic illnesses, degraded sleep conditions combine differently in each person. No single factor explains an episode, and none predicts one.
The popular explanation through a simple "serotonin deficiency", by contrast, is now contested: the literature has largely moved away from the idea of one measurable chemical imbalance. That does not make the treatments ineffective, since their efficacy is judged on clinical outcomes rather than on the accuracy of the story used to present them.
Prognosis, finally, cannot be read off the diagnosis. Some people have a single episode, others several, separated by long stretches without symptoms. How long an untreated episode lasts varies a great deal, and appropriate care generally shortens it.
What treatment actually means
Care rests on two pillars, often combined. Structured psychotherapies, among them cognitive behavioural and interpersonal therapy, have shown their effectiveness for mild to moderate episodes. Antidepressants are useful mainly in moderate to severe forms. Their effect takes several weeks to build, which explains a lot of premature stopping, and both starting and stopping are decisions made with a doctor.
Sleep rhythms, physical activity and keeping a minimum of social contact do not replace treatment, but they count, and they are hardest to sustain exactly when the episode is active.
One point allows no vagueness: suicidal thoughts are among the possible symptoms, they are common and they are nothing to be ashamed of. They should be told to a health professional, and distress that has become unbearable calls for immediate contact with a doctor or emergency services. No article, no loved one and no method found online replaces that assessment.
... and romantic life
Being in a relationship during an episode is possible, and many people are. What tests the relationship is almost never the mood itself, it is how the mood gets read. An episode reduces available energy, not attachment: withdrawal, silence or lowered desire get taken for loss of interest when that is not what they are.
A few markers help more than long explanations. Say what is possible today and what is not, without turning it into a verdict on the relationship. Keep apart what comes from the episode and what comes from the couple, because blending the two eventually makes any ordinary conversation impossible to have. Offer without pushing, since insistence mostly produces guilt. And accept that a partner can lighten daily life and stay present without being the clinician or the treatment.
A partner has limits too, and hiding them protects no one. A relationship resting entirely on the other person getting better wears out, and looking for support for oneself is legitimate.
As for when to bring it up, there is no rule. The diagnosis says nothing about personality, about the capacity to love, or about how long a relationship can last.