A sysmed or
system medicalist is someone with an overly-medicalized view of plurality and systemhood; and who enforces that view onto others. This is most commonly associated with false beliefs that someone can't be plural (having multiple people, personality states or other entities in one body) without a mental disorder or trauma, but also extends to beliefs like "headmates/alters are parts, not people."
The term is derived from transmedicalism, an exclusionist ideology that holds that transness is inherently a mental disorder and that any
trans person who doesn't experience gender dysphoria can't actually be
transgender.
Despite being frequently presented as scientific fact, sysmed claims tend to lack support by actual scientists, who almost unanimously acknowledge the existence of other forms of plurality. (Such as the World Health Organization's ICD-11 stating that you can have multiple "distinct personality states" without a disorder.)
Because of this,
system medicalism can be considered a type of pop
psychology, being popularly presented as scientifically sound despite
lacking any actual scientific basis or merit.