The problem of deciding contractability of closed curves in a topological space is a fundamental problem in (computational) algebraic topology. In 3-manifolds, for simple curves on the boundary, the normal surface theory, as developed by Haken can be used to decide contractability. We present the first algorithm for this problem for closed curves on the boundary of 3-manifolds with self-intersections. The algorithm is based on the proof of the well-known Loop theorem and runs in exponential time.