Aggression

Amygdala

The threat detector. Dense in androgen receptors, and the structure most implicated in the anger, vigilance and fear side of what these compounds do. Splitting it out of the limbic system matters because threat processing and reward processing sit in the same blob otherwise, and compounds pull them in opposite directions.

Executive Function

Planning, switching between tasks, and holding back a response you are about to make. The last of those is the one that matters here: reported aggression on these compounds is often better described as a failure of the brake than as an increase in anger.

Serotonin Signalling

How strongly serotonin is signalling. The system most often named when 19-nor androgens are linked to impulse control, irritability and sleep. Almost all of the evidence is rodent work; nothing has been measured at these receptors in a human on these compounds.