I have a 15 year old son - single parent his entire life.
His father has been inconsistent and noncommittal with him from day 1.
In 7th grade he had huge issues - I took him to a psychiatrist. Got him on Zoloft and into therapy with a licensed clinical social worker.
He was also diagnosed with inattentive ADD at that time - which I had suspected for a few years but was in major denial about.
He began taking focalin for the ADD, but stopped the zoloft as his depression was not organic, rather environmental, and with therapy no longer needed the mood elevator.
Fast forward a couple of years, therapy has ended with the "blessing" of the therapist, and he begins to have major mood swings and rages. At the end of my rope one weekend I pop a Zoloft into him. By the end of the week both he and I notice a considerable difference in his behavior and emotional control. Off to the doctors we go to get their "blessing" to put him back on the Zoloft.
He is now 15, and takes 50 mg of zoloft daily. This past summer he wanted to try a lower dose, so we did that, and after three weeks, he choose to go back on the 50mg. In his words "I like myself better when I take it; I feel better". See, depression and bi-polar run in my family - though I have "escaped" the loop, I am not sure that my son has - I think he suffers from a mild organic depression that manifested itself when puberty hit full force - his doctors agree.
For us, therapy helped him deal with the feelings of loss, and abandonment, and all the other icky stuff his miserable father gave to him and medication has helped him deal with the inherited organic depression.
Talk to the therapist that he seeing - it may be time to find another that your son will relate better to. Explore group therapy for him - sometimes realizing that peers have the same issues helps. Make the doctors do an evaluation and ensure that he is not developing any inherited bi-polar issues as they usually manifest during the early/mid teens.
If the meds he is on now are not helping him - talk to the doctors about trying different ones. If you decide to take him off medication entirely, be sure you do that with the doctors guidance and some of these drugs you cannot just quit cold turkey - they have to be weaned off them.
Medication works to a certain extent but sometimes it just masks the problems. Getting to the emotional root of the problem in order to get it out is the long term solution.
I wish you luck - it is so hard when our children are hurting.