Zyprexa is an atypical antipsychotic and I think all of them are known to cause short term memory loss. I don't know much about lithium however.
Hi, I have taken those two medications together before but I was also taking an antidepressant at the time as well. Which with my rapid cycling bipolar I shouldn't have been taking, this shouldn't affect how I found these two medications but I thought I should give all relevant information.
Lithium affected my memory a lot, sometimes functioning for me was an issue as it made me at times feel like a zombie aswell.Although medications affect everybody differently as I'm sure you know,
Could it also be part of how his illness affects him too, I noticed from an early age ( I have had diagnosed rapid cycling bipolar since I was 13 years old) that my memory recall became really badly affected, I went from a straight A student to having to work extensively when I took my exams just to gain D and E passes. The part of my brain that I used to recall things had been affected by illness greatly. After taking the above two medications my memory became worse but so did my illness so they might effect each other.
I hope that's helped a little, keeping an eye on it is advisable and please do take that maybe your sons illness is a possibility contributing factor into account too. Medications and etc treatment have really affected all parts of memory now, side effects are always possible but only you and your son can decide whether the benefits that the medication give do not out weigh the the side effects you are getting. You don't mention how new your son is to this combination, maybe it will settle down but my best advice would be inform your Pdoc as they need to be aware of any side effects that are a problem they may decide that he would benefit from changing either the dosage or change a medication altogether.
Keep in touch and let us know how you are getting on.