Simply provide heroin, and lots of these people would self-execute. The cops collect lots of heroin, and they don't have any use for it. The disposal costs must be annoying. It seems we can solve the problem of disposal as well.
Except maybe in some countries where doctors dish out opioids like they are candy.
In some cases, it's essentially identical to drugs used in hospitals. In the UK, diamorphine is commonly used in palliative care.