Like symptoms other than the obvious ones like feeling down.
When does someone get the point where help from medication is needed. I know someone who is suffering from a form of depression but is worried that the antidepression tablets will have worse side effects. its hard to know if its severe depression or even depression at all.
Change of appetite
Change of sleeping patterns, sleeping more or less
Not doing things you used to do/becoming withdrawn and being bored
Fatigue
Doing the little things become harder
Anxiety
You feel guilty for being a burden and feel like a failure
You look at the negative most of the time and can't think clearly.
You feel lost in this world and life is passing you by.
Unexplained physical pains, headaches, back pain etc.
Change in personal hygiene and appearance
Crying easily, feeling alone.
The doctor can do blood tests to see if there are physical reasons why a person may be depressed, i.e a chemical imbalance in the brain. Depression does not neccessarily have to be treated with medication though. A psychologist can work through the feelings and work with the person to improve.
Also, there are lots of websites with information on depression.
There are several online resources for depression screening.
findingstone.com/services/tes…
med.nyu.edu/psych/screens/dep…
depression.medgrip.com
By using one or all of them you can have some basic idea.
bostonchick and John L provide solid guidance.
When I was telling my friends I had been diagnosed with depression, a couple of them said they'd seen signs that something was wrong but weren't sure they should tell me. I'm glad you're there to help this person out.
hopeless
alienation from friends and family
change in appetite
suicidal thoughts
feeling tired all the time
sleep pattern differs
anxiety
doesnt take care of oneself
everybody has the blues sometimes..but when it last more than week..thats when you need to seek help
When you stop doing the things you enjoy doing, and secluding yourself from your friends and the world, it's time to get on medication.
: im basicly doing everything the 1st answers says 
also if you are under 18 medication is not recommend but there is exceptions