Since 2000, 75% of US opiate users started with prescription drugs[1]. So my guess is overdoses would be substantially worse if any opiate was freely available over the counter.
[1] - https://nida.nih.gov/publications/research-reports/prescript...
but the rate of overdoses from prescription opiates is, as i understand it, very low, because the dosage is predictable
a lot more old people needing regular enemas would be kind of shitty but not nearly as bad as millions of people dying from overdoses
Over time, addicts do not get the same high from the same dose of opiates. They require higher dosages, until such a point where they have to turn to illicit narcotics (which are also cheaper). Prescription drug abusers are 40x more likely of becoming heroin abusers.
This is all in the article I linked above (click on the subheadings).
this would increase the risk of suicide, but it would have to rise a lot to exceed the current usa rate of accidental overdose deaths