When a drug is used off-label, it's because a physician makes a decision in a specific patient when this drug would be, on a population level, contraindicated. Maybe because that patient is allergic to other available therapies or has not tolerated the other available therapies, the physician might make the decision to use that drug in that specific patient, outside the approved indication. That doesn't mean there is no medical rationale behind it, but just that it's outside what has been approved on a population basis.
On May 1st, 2008. See this statement in context.