MDD stands for major depressive disorder, and its diagnosis requires at least five specific symptoms lasting for a minimum of two weeks, with at least one of those symptoms being persistent low mood or a loss of interest in nearly all activities. It’s the clinical term for what most people simply call depression, affecting roughly 5.7% of adults worldwide. But an MDD diagnosis isn’t just a label for feeling sad. It’s a structured evaluation designed to confirm the pattern, rule out other causes, and guide treatment.
The Nine Symptoms Clinicians Look For
The diagnostic criteria come from the DSM-5, the standard reference used by mental health professionals. To qualify for an MDD diagnosis, you need five or more of the following symptoms present during the same two-week period, and they must represent a change from how you normally function:
- Depressed mood most of the day, nearly every day. In children and adolescents, this can show up as irritability rather than sadness.
- Loss of interest or pleasure in almost all activities, even ones you used to enjoy.
- Significant weight change of more than 5% in a month without trying, or a noticeable shift in appetite up or down.
- Sleep problems, either insomnia or sleeping far more than usual.
- Observable physical changes in movement, either restless agitation or being noticeably slowed down, to the point that other people can see it.
- Fatigue or low energy that makes even routine tasks feel harder to complete.
- Feelings of worthlessness or excessive guilt that go beyond normal self-criticism.
- Difficulty thinking, concentrating, or making decisions.
- Recurrent thoughts of death, suicidal thinking, or suicide attempts.
At least one of your five symptoms must be either depressed mood or loss of interest. You could have severe fatigue, weight loss, insomnia, and difficulty concentrating, but without also experiencing low mood or loss of interest, the diagnosis wouldn’t apply. That requirement anchors the diagnosis to the core experience of depression rather than a collection of symptoms that might point elsewhere.
How the Diagnosis Actually Happens
There’s no blood test or brain scan for MDD. Diagnosis is a multistage process that pulls together your clinical history, a physical exam, and sometimes lab work. It typically starts with a conversation. A clinician will ask about your mood and interest in daily activities, and if those answers raise concern, a more detailed diagnostic interview follows.
Many providers use a screening questionnaire called the PHQ-9 as a starting point. It’s a nine-item form that maps directly to the DSM-5 criteria, with each symptom scored from 0 (not at all) to 3 (nearly every day). The total score falls into severity categories: 0 to 4 is minimal, 5 to 9 is mild, 10 to 14 is moderate, 15 to 19 is moderately severe, and 20 to 27 is severe. A score of 10 or above generally signals that a full clinical evaluation is warranted.
The PHQ-9 is a screening tool, not a diagnosis by itself. After screening, the clinician digs deeper: how long the symptoms have lasted, how much they interfere with work and relationships, whether there’s a family history of mood disorders, and whether anything else might explain what you’re experiencing.
Conditions That Must Be Ruled Out First
One of the most important parts of an MDD diagnosis is making sure the symptoms aren’t caused by something else. Depression symptoms can look identical to a surprisingly long list of medical problems, and treating the wrong cause means treatment won’t work.
Thyroid disorders are a common culprit. Both overactive and underactive thyroid glands can produce mood changes that mimic depression, and subclinical hypothyroidism (a mild form that’s easy to miss) shows up in 4% to 40% of people with mood disorders. When hypothyroidism goes undiagnosed, it’s one of the leading causes of depression that doesn’t respond to standard treatment. The good news is that correcting the thyroid imbalance often resolves the mood symptoms entirely.
Other medical conditions on the checklist include diabetes, Parkinson’s disease, multiple sclerosis, vitamin D or B12 deficiency, iron or folate deficiency, and even certain infections. Medications can also trigger depressive symptoms, including steroids, some blood pressure drugs, anticonvulsants, and sedatives. Alcohol use and stimulant withdrawal are also known to cause depression-like episodes. This is why many clinicians will order bloodwork during the evaluation, checking thyroid function, nutrient levels, and other markers before confirming an MDD diagnosis.
Bipolar disorder is another critical rule-out. If you’ve ever had a manic or hypomanic episode, the diagnosis shifts from MDD to bipolar disorder, even if your current symptoms look exactly the same. The distinction matters because the treatments are very different, and some medications used for MDD can actually worsen bipolar disorder. Your clinician will ask about past episodes of unusually high energy, reduced need for sleep, impulsive behavior, or periods of feeling “on top of the world.”
Severity and Specifiers
An MDD diagnosis isn’t one-size-fits-all. Clinicians add specifiers that describe the particular pattern of your depression, which helps guide treatment choices.
Depression with anxious distress is one of the more common patterns. It’s marked by feeling keyed up or tense, unusual restlessness, difficulty concentrating because of worry, fear that something awful is about to happen, and a feeling of losing control. Severe cases often include visible physical agitation. This specifier matters because anxiety-dominant depression can respond differently to certain treatments than depression without prominent anxiety.
Melancholic depression describes a pattern with profound loss of pleasure in nearly everything, along with observable physical changes. People with melancholic features often have both agitation and slowed movement, a distinct quality of sadness that feels different from grief, and symptoms that are typically worse in the morning. This type of depression tends to respond better to certain treatment approaches than others.
Other specifiers include atypical features (where mood can temporarily lift in response to good news, and symptoms like increased sleep and appetite dominate), seasonal pattern (episodes that consistently appear in fall or winter), and peripartum onset (depression starting during pregnancy or after delivery).
What a Diagnosis Means for You
Getting an MDD diagnosis can feel heavy, but it serves a practical purpose. It’s the step that opens the door to structured treatment, whether that’s therapy, medication, or a combination. It also gives your clinician a framework for tracking whether you’re getting better. The severity rating from tools like the PHQ-9 provides a baseline number that can be compared over time as treatment progresses.
MDD can be a single episode or recurrent. Some people experience one depressive episode triggered by a specific life event and never have another. Others cycle through episodes over years or decades. Your clinician will factor your history into a longer-term plan, especially if you’ve had previous episodes, since the risk of recurrence increases with each one.
The two-week minimum for symptoms sometimes leads people to wonder whether they should wait before seeking help. You don’t need to time it. If your mood or functioning has shifted noticeably and it’s interfering with your daily life, that’s enough reason to start the conversation. The two-week threshold is a diagnostic guideline, not a waiting period you’re expected to endure before reaching out.