Psychology Today: Can Aggression Signify Depression?

"Depression, like many mental illnesses, has an inaccurate stereotype. The deflated, sobbing, suicidal profile depicted in popular culture is not untrue, but it is by no means the only depressive experience.

Aggression is not an unusual indicator of depression. So prevalent this is, that, in 2001, the researcher van Praag suggested a new depression diagnostic consideration based on unique biomarkers behind many people who tend to be aggressive while depressed.

Perhaps the closest the DSM-5 (page 163) comes to recognizing aggression as a symptom of depression is noting that irritability, described as "... persistent anger, a tendency to respond to events with angry outbursts or blaming others, or an exaggerated sense of frustration over minor matters," is not uncommon.

If it is not recognized that the aggression may be a sign of depression, chances are treatment will focus on "anger management," which will provide some coping skills, providing tenuous stability at best. The anger, like a weed, will grow back because its root, the depression, has not been eradicated.

How depression and aggression are related

1. Neurochemistry: It's no secret that lower levels of serotonin, a serenic, "down-regulating," or "feel-good" neurochemical, is associated with the dysphoria (unpleasant mood) of depression. It has also been long known that depression is correlated with disruptions in the hypothalamic-pituitary-adrenal (HPA) axis, which governs hormones, which help govern mood, aggression, sleep, and appetite.
2. Poor sleep: Depressed people tend to experience insomnia, and it is well-documented that insomnia and irritability/anger are associated (e.g., Saghir et al., 2018; Kim et al., 2019). Poor sleep is associated with elevated amygdalar reactivity (e.g. Prather et al.; 2013; Saghir et al., 2018), which, given the amygdala regulates response to threats, not uncommonly is in the form of anger/aggression.
3. Appetite disturbance: People with depression tend to experience appetite changes, often in the form of eating less. Brains need a particular amount of glucose to function, and if sufficient food isn't ingested to sustain this, the body releases hormones that contain glucose (e.g., Cleveland Clinic, 2021). Two of these are the excitatory hormones cortisol and adrenaline, which are associated with inflamed tempers.
4. Stimulation-seeking: As written about in An Unusual, Overlooked Sign of Depression, while depression and excitement seem like strange bedfellows, some depressed individuals discover that they can perk themselves up by engaging in thrill-seeking activities, including fighting.

Treatment implications