A lot of the overdoses you're seeing these days is because people are receiving drugs contaminated with fentanyl when they're expecting just oxycodone or heroin. The lethal dose of heroin is about 30mg, whereas the lethal dose of fentanyl is 3mg. It does not take much contamination to kill you. A prominent example of a fentanyl death is Mac Miller. Fentanyl has also been found in batches of cocaine and ketamine, and also has caused accidental overdoses that way. Overdoses can also happen when you are used to a relatively impure product and one day receive a much more pure version.
I know addicts, and I know the issues at play here. Do tell me again how legalizing / regulating drugs wouldn't help greatly reduce overdoses.