Tylenol (acetaminophen) is the base in many opioid pain meds. (Darvon, Vicodin, etc.)
Acetaminophen can literally kill somebody in a fairly short time, due to liver damages.
A person taking their opioids as prescribed, then supplementing that with Tylenol, could easily go beyond the max acetaminophen per day.
We have a family friend, that lost a son that way. Gone, dead in his 20s.