How can i prevent my friend from sniffing dendrite (a glue consisting toluene and other intoxicants)?

You can't: The best you can do is be a friend. Nagging a person to give up something they probably already know isn't wise doesn't help and gets resented. Offer that person something better to do. There is nothing good about sniffing glue, but most people don't die of it and probably don't even get seriously damaged. Don't endanger the friendship -- you may be this person's one true friend after all.