@oralloy,
The local clinic which deals with mental illnesses ranging from clinical depression to schizophrenia and all manner of "danger to themselves or others" behavior has a list and in many cases, adds these to the list of people who should not be able to purchase firearms.
I have been called to situations you would not believe and each of those people did not possess the mental capacity to know right from wrong one minute to the next. You do not want everyone to have the ability to buy a gun. From the depression angle, suicide should be a concern.
If it is situational depression - and the person wants a gun - there is a process they can follow to earn that ability.