The five mood disorders most commonly referenced in mental health are major depressive disorder, persistent depressive disorder, bipolar I disorder, bipolar II disorder, and cyclothymic disorder. These aren’t the only mood-related diagnoses in the clinical manual (the DSM-5-TR includes several others, like premenstrual dysphoric disorder and mood disorders caused by medical conditions), but these five form the core categories that most discussions of mood disorders center on. Each one involves a distinct pattern of emotional disruption, from prolonged sadness to dramatic swings between highs and lows.
Major Depressive Disorder
Major depressive disorder, often just called depression, is the most prevalent mood disorder. An estimated 21 million adults in the United States had at least one major depressive episode in 2021, representing 8.3% of the adult population. Women are affected at nearly twice the rate of men: 10.3% compared to 6.2%.
A diagnosis requires at least five symptoms present during the same two-week period, and one of those symptoms must be either a persistently depressed mood or a noticeable loss of interest or pleasure in activities you previously enjoyed. The other possible symptoms include significant changes in weight or appetite, sleeping too much or too little, physical restlessness or feeling slowed down, constant fatigue, feelings of worthlessness or excessive guilt, difficulty concentrating or making decisions, and recurrent thoughts of death or suicide. These symptoms need to be a clear change from how you normally function and severe enough to interfere with work, relationships, or daily life.
Depression isn’t just feeling sad for a few days. The key distinction is duration, intensity, and impact. Nearly everyone experiences low moods, but major depressive disorder persists most of the day, nearly every day, and makes it genuinely difficult to keep up with responsibilities or find enjoyment in anything.
Persistent Depressive Disorder
Persistent depressive disorder, previously called dysthymia, is a chronic form of depression that lasts at least two years in adults (one year in children and adolescents). The depressed mood is present most of the day, on more days than it’s not, for that entire stretch. Many people describe it as feeling like a low-grade fog that never fully lifts, rather than the intense episodes seen in major depression.
Despite its reputation as the “milder” form of depression, persistent depressive disorder can be just as disabling as major depression, and in some cases more so. A 10-year study found that people who had both persistent depressive disorder and major depressive episodes experienced greater severity of depression, anxiety, and physical symptoms than those with major depression alone. You can, in fact, be diagnosed with both conditions at the same time, a situation sometimes called “double depression.” The longer duration of persistent depressive disorder tends to erode social and occupational functioning gradually, making it easy to mistake for a personality trait rather than a treatable condition.
Bipolar I Disorder
Bipolar I disorder is defined by the occurrence of at least one manic episode. Mania involves a period of abnormally elevated, expansive, or irritable mood combined with increased energy or activity. During a manic episode, a person might sleep very little yet feel rested, talk rapidly, take on ambitious projects, spend recklessly, or make impulsive decisions that are out of character. In severe cases, mania can include psychotic features like delusions or hallucinations, and it often requires hospitalization.
Most people with bipolar I also experience depressive episodes, but they aren’t required for the diagnosis. The defining line is mania: if a full manic episode has occurred, the diagnosis is bipolar I regardless of whether depressive episodes are also part of the picture. Manic episodes typically last at least a week, or any duration if hospitalization is needed.
Bipolar II Disorder
Bipolar II disorder involves a pattern of depressive episodes alternating with hypomanic episodes. Hypomania is a milder form of mania. It involves the same type of elevated or energized mood, but it’s less severe, doesn’t include psychotic features, and doesn’t require hospitalization. A hypomanic episode lasts at least four days.
Bipolar II is not simply a less serious version of bipolar I. People with bipolar II tend to spend more of their time in depressive episodes, and the depression can be severe and prolonged. The condition is also harder to catch early because hypomania can feel productive and pleasant, both to the person experiencing it and to those around them. Clinicians and patients alike often miss hypomanic episodes, especially early in the illness, which means many people with bipolar II are initially misdiagnosed with major depression. The distinction matters because the treatment approach for bipolar depression differs significantly from the approach for unipolar depression.
Cyclothymic Disorder
Cyclothymic disorder, or cyclothymia, involves chronic, fluctuating mood disturbances with periods of hypomanic symptoms and periods of depressive symptoms that don’t meet the full criteria for a hypomanic or major depressive episode. These fluctuations must persist for at least two years in adults (one year in children and adolescents), with symptoms present for at least half that time and no symptom-free stretch lasting longer than two months.
What distinguishes cyclothymia from ordinary moodiness is its intensity, persistence, and reactivity. People with cyclothymia experience rapid and intense mood shifts in both directions. Positive events can trigger disproportionate euphoria and impulsiveness, while even minor stress can spiral into unusual sadness, extreme fatigue, or feelings of desperation. This emotional dysregulation, the tendency to over-react to external events especially in relationships, represents the core of the condition. Because the symptoms don’t reach the threshold of full mania or major depression, cyclothymia often goes unrecognized for years, but it carries real consequences for relationships, work stability, and overall quality of life.
What These Disorders Have in Common
All five mood disorders share a disruption in the brain’s chemical signaling systems. Serotonin, norepinephrine, and glutamate are the primary chemical messengers that regulate mood, and imbalances in these systems play a role across the spectrum. Dopamine, which drives the brain’s reward circuitry, is particularly relevant in bipolar disorders, where abnormal signaling in reward pathways may contribute to the euphoria and risk-taking behavior seen during manic and hypomanic states. Inflammation also appears to play a connecting role: inflammatory processes in the body can alter how these chemical messengers are produced and recycled, which helps explain why mood disorders so often co-occur with chronic physical illnesses.
Treatment for mood disorders generally falls into two broad categories: medication and psychotherapy, often used together. Depressive disorders are typically treated with medications that increase the availability of serotonin or norepinephrine in the brain, combined with structured therapy approaches like cognitive behavioral therapy. Bipolar disorders require mood-stabilizing medications, and the treatment strategy is more complex because medications that help depression can sometimes trigger manic episodes. Cyclothymia is the least studied of the five, and treatment often focuses on mood stabilization and learning to manage emotional reactivity.
Other Mood-Related Diagnoses
The DSM-5-TR includes several additional mood-related conditions beyond these core five. Premenstrual dysphoric disorder (PMDD) causes marked mood swings, irritability, depressed mood, or anxiety in the week before menstruation, improving within a few days after a period starts. It affects a smaller percentage of menstruating people than typical PMS but is significantly more disruptive, requiring at least five symptoms that interfere with daily functioning.
Disruptive mood dysregulation disorder (DMDD) applies to children between ages 6 and 17 who experience severe, frequent temper outbursts (three or more times per week) alongside a chronically irritable or angry mood most of the day, nearly every day, for at least 12 months. This diagnosis was created partly to address concerns about overdiagnosis of bipolar disorder in children. As children with DMDD grow older, their symptoms often shift toward depression or anxiety rather than developing into bipolar disorder.
There’s also depressive disorder due to another medical condition, which recognizes that conditions like thyroid disorders, stroke, or Parkinson’s disease can directly cause depressive symptoms through their biological effects on the brain, not just as a psychological reaction to being ill.