It seems to be the fashion now to attribute high crime rates and mad monarchs to heavy metal poisoning (lead, arsenic, mercury, etc.).
What happens if the dangerous effects of these metals are discovered much earlier? The Point of Divergence can vary, but for the sake of example, let's say an astute Greek alchemist from Alexandria, Egypt finds out? That seems to be the earliest time for Western alchemy (you can use Eastern alchemy if you prefer).
(Or were the effects known earlier, and people simply ignored it? This could be the case given leaded gasoline and Paris Green paint).
Correct me if I'm wrong on any of these points.