Like when a plant is being grown you put a fence around to protect the plant. In the same way we must protect the young minds, with certain mental barriers. This is essential. We have to give them certain concepts by which they do not move an inch in that direction.
For those who are already addicted, to bring them out, there are three ways: Love, Greed and Fear. If they love someone then ask them to take a vow or promise on their loved one that they will never touch it again. Or tell them that you will have so much more luck if you don’t touch these addictive substances.
Help them in whatever manner you can to come out of it. There are many remedies in Homeopathy and in Ayurveda. Yoga and meditation are also very good. I have seen millions of people come out of their addictions just by doing some yoga and meditation.