Mental health disorders can still be caused by an underlying physical change in brain structure or chemistry. Dementia is an example of a mental health disorder. The most common cause of dementia is Alzheimer's disease, which is due to physical changes of the brain.

Addiction is undeniably a mental health disorder which has physical underpinnings. As often are other mental health disorders such as depression, which can be related to hormonal or chemical changes in the brain. In fact, I would argue very few mental health disorders have no physical alterations to the brain - functional neurological disorders being the only ones I can think of off the top of my head (and this is more like a category of poorly understood disorders than a single disease).