Interesting thing that using/abusing substances to deal with anxiety can actually produce more anxiety. And, anxiety is often caused by fear.
So, whenever I feel anxious I'm tryimg not to run away from that feeling, but ask myself: "What's got me feeling so anxious? What am I afraid of?" And...be prepared to truly DEAL with the answers to those questions.
Also, withdrawing from an addictive substance can produce anxiety. It's one of the hallmarks and one of the first signs a person might show: anxious, on edge, etc. (because they didn't get their fix)...