The clinical features of excessive doses of opiates include coma of varying severity, small pupils and depressed respiration.
As the medical profession grew in expertise and stature, their calls for legal controls on opiates and cocaine became more authoritative.
In a known drug user, sweating, involuntary sniffing and pupillary dilation are helpful physical signs of early withdrawal from opiates.
The evidence that the body's own opiates cause exercise-induced euphoria is even less clear cut.
Instead of accepting dogma, perhaps one ought to think through problems including the problem of prescribing opiates.