What is the difference between forced intervention and whatever Portugal did when it decriminalized hard drugs?
Portugal treats it as a mental illness health issue, and provides counselling. Only large non-personal amounts are treated as distribution, and therefore, criminal.
Only mental heath professionals can assign intervention, and typically only in cases where the user is a viable threat to themselves or others (imminent danger of harm through violence). This means that the vast majority of users are not coerced at all - they enter into counselling willingly, and with an intent to come clean.
The reason why things have backslid in the last little while has been due to funding cuts, and nothing else. Which is the same as any public service -- funding determines effectiveness.