It is not the meds that do it; it is known to be one of the very first symptoms in unmedicated people with sz or in the prodrome. That was my son’s first and primary symptom. It persisted for ten years. When he was a teenager he was really high-achieving, but in his prodrome he dropped out of med school, then spent ten years never finishing anything - almost never finishing anything. He is slowly getting better. He has support from an Early Intervention Team. But CBT has helped. He tends to say he has done nothing in ten years and he is a failure. So I point out the things he has done and finished (usually short courses, things to do with art, his religion, etc). He has learned to cook very well, for example. He also lives independently and has done various very nice bits of work on his flat. In the last two years he has been on risperdone - which was disastrous because it knocked him out too much. Then he was on Ability for a while, which did help, and he did more. Then he came off it and had a huge long depression. Now, he is on serotonin re-uptake inhibitors and he seems to be getting more active again. He is doing more work on his flat, doing some weight training (so I guess eating better) and has enrolled on another course. When he was very depressed I went to stay with him for a month and cooked etc for him and kept him company (social withdrawals probably his biggest problem). the we went together to visit family, or they came to visit us. We went out together and bought furniture etc. Went to parks and so on.
So doing stuff together can be a start. Start with really tiny tasks. People with sz talk themselves down a lot. Plus, apparently they find it hard to anticipate enjoyment. I believe that people can probably “retrain” themselves. I actually made my son stand and look at some of the work he has done on his flat, and told him, “Look at it every day and think ‘I did that. That’s good.’” I hope it will reinforce his “pleasure circuits” and his confidence to do more stuff.
I admit here that my son doesn’t have a full sz diagnosis. He has had psychosis a couple of times, but always with insight so he’s still on the borderline of having a “psychotic depression” diagnosis. Anyway, his positive symptoms are not very strong or frequent. His struggle has been ore with the negative ones. But for me, yes, the most significant one is the motivation one. Because it is a vicious circle. The less he achieves, the more he berates and hates himself and then he destroys his own self-esteem and confidence. But he is getting better (I pray).