Jayne,
I have a son 10 who was on lithium this year and it was not effective for him at all. It actually caused him to have ticks and he almost acted as if he was drunk. This was after we increased it and it was not good. I took him that day to his doctor's office and showed the psych. what was happening to him physically, even the doc looked concerned.
If his speech is slurry and he is acting different demand that his doctor knows keep calling, keep pestering until you get help. Lithium can get to toxic levels. You are right to be concerned!
Ginny
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