What is the medical model in psychology?

It is a model that assumes, that every mental illness has its biological (physiological) basis-- it's an effect of chemical inbalance in the brain, physical abnormality in the brain or genetical abnormality.

According to the model treatment of mental disorders should include medicines, electro-convulsive therapy (ECT) and psychosurgery.

A disadvantage of the model is that does not take into account psychological problems underlying an illness. Additionally, drugs do not cure the illness, they only give a temporary relief from the symptoms.

Medical model treatment is certainly helpful, but it should not be the only way of treating mental disorders-- it needs to be combined with some sort of psychotherapy (e.g. cognitive-behavioural etc.)