Hyperthymic temperament, or hyperthymia, from Ancient Greek ὑπέρ ("over", meaning here excessive) + θυμός ("spirited"), is a proposed personality type characterized by an exceptionally, or in some cases, abnormally positive or irritated mood and disposition. It is generally defined by increased energy, vividness and enthusiasm for life activities, as opposed to dysthymia. Hyperthymia is similar to but more stable than hypomania.

Characteristics of the hyperthymic temperament include:

These features typically onset early in life (adolescence or early adulthood) and are relatively stable over time. In practice, hyperthymic temperament is often assessed with standardized temperament questionnaires such as the TEMPS-A, which measure it as one of the affective temperament dimensions.

Many individuals with hyperthymic temperament function well and excel in occupational and social roles. Their elevated mood and energy levels can contribute to career success and relationship stability. Hyperthymic traits such as confidence and high motivation are potentially advantageous. They are linked to a reduced risk of suicidal behavior and fewer hospitalizations among patients who develop mood disorders. Hyperthymic temperament appears to exert a protective effect against several psychiatric conditions. Individuals scoring high on hyperthymic temperament are less likely to experience unipolar depression, dysthymia, or anxiety disorders. It shows little to no comorbidity with major depression, indicating it may serve as a buffer or resilience factor against depressive illness. Among bipolar patients, hyperthymic temperament is associated with a later age of onset, milder illness course, and fewer suicide attempts, indicating a generally better prognosis. This temperament may promote greater resilience and effective coping strategies, due to the combination of high energy and a positive appraisal style.

Hyperthymic temperament shares similarities with bipolar spectrum disorder. Individuals with hyperthymic temperament maintain an elevated mood baseline but may transition into depression or mania. If a person with hyperthymic temperament experiences a major depressive episode, their history of persistent elevated mood may indicate an underlying bipolar tendency. American psychiatrist Akiskal termed this scenario "bipolar IV" – depression superimposed on a hyperthymic temperament. In such cases, what may appear to be a consistently optimistic personality precedes the onset of mood episodes, potentially evolving into a bipolar pattern. While hyperthymic traits are protective against unipolar depression, they do not protect against bipolar mania. Hyperthymic temperament may predispose individuals to manic or hypomanic episodes. There is a genetic association between hyperthymic temperament and Bipolar I disorder, and clinically, hyperthymic features (such as reduced sleep need and impulsivity) may precede full manic episodes. There is also an association with substance use and risk-taking behavior – hyperthymic individuals may be more prone to substance misuse during mood episodes, reflecting their stimulus-seeking tendencies. When individuals with hyperthymic traits become depressed, standard antidepressant medications may be problematic: due to underlying bipolar spectrum neurobiology, antidepressants alone may be ineffective or may trigger mixed features or mania. Mood stabilizers or treatments targeted toward bipolar disorder are considered more appropriate in such cases.

Hyperthymic temperament is associated with dysregulation in brain dopamine pathways. In particular, the mesolimbic dopamine pathway (ventral tegmental area projecting to the nucleus accumbens in the ventral striatum) and the mesocortical pathway (projections to frontal regions like the orbitofrontal cortex) are implicated. These pathways govern reward processing, motivation, and mood regulation. Neuroimaging evidence shows that reward-related circuits including frontostriatal regions such as the ventral striatum and orbitofrontal cortex tend to be more active in individuals with hyperthymic temperament. Such findings support the view that hyperthymic temperament involves dopaminergic hyper-responsivity in reward networks, although not to a pathological degree.

Functional Magnetic Imaging (fMRI) study identified that Individuals with hyperthymic temperament showed distinct functional connectivity in regions such as the prefrontal cortex, anterior cingulate cortex (ACC), amygdala, thalamus, and hippocampus. These neural patterns were dissimilar from those of individuals with cyclothymic, irritable, or anxious temperaments, which tended to cluster together.

fMRI research has found that individuals with higher hyperthymic trait levels exhibit altered activation in reward-related brain circuits. During anticipation of non-monetary rewards, people with higher hyperthymic temperament show reduced activation in the premotor cortex, whereas performance feedback elicits heightened responses in sensory-related areas proportional to their hyperthymic scores. The brains of hyperthymic individuals appear to respond more robustly to actual positive outcomes while requiring less activation during anticipatory phases. This profile may reflect differences in how positive emotions are regulated and processed in the brain.