If nobody asked for your advice, it is better to remain silent.
Especially if you have never been a drug addict, an alcoholic, or codependent to a person suffering from these conditions.
The best help is to avoid being an obstacle to others.
Do not lecture anyone about how bad drugs are or how much they are wasting their lives by snorting, inhaling or drinking toxic substances.
However, if you really care for your friend, sibling or partner, let them know that rehab does not equal torture. There are state of the art facilities like La Jolla Recovery in San Diego ready to help them.