Rosenhan, what a classic study! Oh, which reminds me, if you're using AS studies for G544 (I did, my teacher said it would be easiest) then make sure you keep revising them throughout the year
You do learn about lots of types of mental disorders, so things like psychotic disorders. You also learn about diagnosis, so about the ICD diagnostic manual in comparison with the DSM, and there is also a study about sex biases in diagnosis (how there is a tendency for doctors to diagnose based on gender rather than actual symptoms).
Dysfunctional behaviour is another big topic which is very similar to disorders. The two cross over a lot (we did the same studies both for treating disorders and for treating dysfunctional behaviour). There is also an emphasis on causes of mental disorders (either dysfunctional behaviour or disorders).
The final other topic we did was stress. This included studies on measuring stress, so using Likert scales etc, and causes of stress (things like lack of control). Even in this topic there were studies using participants with mental disorders. So the vast majority of studies use participants with some sort of mental disorder, but your job is to use the study in relation to treatment of stress or whatever other topic it has been put into (and ultimately manipulate the study in a way which will answer the question).
Hope that helps! If you feel overwhelmed by the sheer volume of studies, just remember that everyone else is in the same boat