Hi.  I think this is something that a doctor or psychologist would have to make a decision about because, while you may know why you're depressed, it can still cause chemical disturbances in your brain that medication could help.  Or, you could have a reason that is situational but also biological, on top of it.  If it's situational, they'll want to know how long you've been depressed and what your symptoms are.  I don't think there's anything that says you shouldn't take them if you know why you're depressed.  I pretty much know why I have depressive episodes, but the medication helps make them be more tolerable and it's not my only source of help.  Sometimes grief can go on for an extended period of time, for example, beyond what someone might consider normal, and if it's interfering in how you function, it might be worth considering medication.

Hope that helped some.