In the U.S. we commonly see waves of "heroin" overdose deaths over the course of a single weekend. I use quotes because it's usually not diacetylmorphine, it's a fentanyl analog. While they're both illegal, fentanyl doesn't require large poppy fields to manufacture, and it can be more easily concealed for smuggling due to the significantly higher potency by weight and volume.
And the cause of those overdose deaths is typically a new illegally smuggled batch of it showing up in a specific area that may or may not be diluted correctly, and even if it is diluted correctly, it may or may not be significantly more potent than the batch that was being sold the day before.
The "normal" fentanyl that we use to control chronic and postoperative pain, and for anesthesia, is active and easily felt at the 12.5-25mcg level. Some of the fentanyl analogs, including some we use in hospitals, are active at less than 1/100th of that. You simply can't see that or handle it safely, so illicit "heroin" is dry mixed with other, ideally inert, powders.
This works fine for things like a cake mix, where the whole thing is going to be further processed with liquids added to it, but for a potentially lethal drug it's extremely dangerous.
As a result, people accidentally take 50x or more than they thought they were taking, and first responders like police and EMS are at serious risk of overdose themselves, simply from touching a surface or a plastic bag that looks empty.
There is virtually nothing we can do to prevent that unless we move the demand into a regulated channel like a pharmacy.
A nice side benefit to distributing the drugs for free, as long as it isn't overly restrictive, is that it can potentially destroy the blackmarket by eliminating the profit motive as well.