I will discuss two effective results about hyperbolic Dehn surgery. The first result is about with cosmetic surgery: namely, distinct long Dehn fillings on a cusped manifold cannot yield the same closed 3-manifold. The second result says that long Dehn fillings yield closed 3-manifolds with large Margulis numbers. These results are effective in the sense that all hypotheses and conclusions (such as ``long'' and ``large'') are explicitly quantified. This is joint work with Jessica Purcell and Saul Schleimer.