Diazepam
"I only use it when I'm having a panic attack (5mg) and it's incredibly effective. Just knowing it's there can be enough to stave off panic. Should never be used for mild anxiety, or used regularly, because it's important to use your own resources to deal with that, and you can become tolerant - but for those occasions when you feel you're losing control, there's nothing more effective that Diazepam. Doctors hate prescribing it - they assume you don't know how to use it responsibly."