One of the biggest problems with drug therapy is that it takes a really long time to get a medication that works, it takes about a month to see if a medication helps or hurts and then you have to adjust for dosage and really when it comes to picking a medication -I'm not even joking about this- it's just guesswork. There are so many different anti-depressants and anti-anxiety medications that doctors just pick a medication and try it out. And with so many different disorders at once, it hints to me that your son’s brain chemistry has a very delicate balance. Because of all of these things I cannot stress the importance of therapy enough. Stick with a medication that helps, but he has to know not to depend on them to "cure" him.
In one of my classes a professor used the most wonderful analogy for mental health and drug therapy. He said that dealing with mental health problems is like being pushed from a raft in the middle of the ocean and not knowing how to swim. Therapy is like someone standing on that raft and trying to teach you how to swim. You can’t listen to their instructions however because you’re trashing around and panicking because your life depends on it. However drug therapy can act as a life preserver. This doesn’t teach you how to swim, it doesn’t solve the problem that you’re in the middle of the ocean and can’t swim, but it allows you to calm down and listen to the instructions on how to swim.
Other than the standardized drug and therapy combinations, the other most important thing in dealing with mental health is a social support system. The consensus in mental health research is that social support is one of, if not the most important protective factors. Be emotionally supportive, listen to his concerns, and try to not lecture him. He will find his way. He just needs you to hold his hand while he looks for a path. However, I HIGHLY discourage self-medication. I myself turned to drugs and alcohol when my anxiety and depression was at its worst and it does NOT help. It may feel like it does at the time, because you get to forget about your problems for a while, but they are still there when the drugs wear off. It creates substance abuse problems and is a form of avoidant coping which is noted in all of the research I study as being one of the biggest predictors of negative mental health outcomes.
tl;dr Drug therapy can be a useful tool, but not a solution. Use this in combination with therapy so he can learn how to function with these disorders. As for helping your son, don't loose hope. He needs you to replenish his. Emotionally supportive and unconditional positive regard are your most important tools. He needs to stop self-medicating and see that he has the strength to get through this and you need to motivate him to see his potential.
I wish you the best of luck with this. If you need any help in dealing with this you can message me or check out /r/depression He's lucky to have a mother so concerned and loving as you.