This is the wrong thread to discuss LPG, but lithium is probably not the only drug he was using, if he was indeed using it. One of his friends (I forget which) told police that LPG was addicted to drugs, and I am pretty sure he was not talking about lithium.
Here it is, found it mentioned in Rick's Blog:
"Elsa described Gonzalez as extremely addicted to prescription meds."
http://ricksblog.biz/?p=7247