no one would take too much Tylenol unless they were suicidal,
"What are the most common poisons for adults? Pain medicines (analgesics) which can be over-the-counter, prescribed, or illegal. Examples include aspirin, oxycodone, acetaminophen, methadone, and ibuprofin." - http://www.aapcc.org/dnn/PoisoningPrevention/FAQ.aspx
but losing control on heroin can cause you to tox up to a lethal amount without even knowing it...
A major cause of heroin OD is variable potency, which could be eliminated with legalization and regulation.
Ok, I get it you want easy to access legal recreational drugs...
Fortunately society is still sane about that...