We present a theoretical study of several hydrogen defects in the upper mantle mineral forsterite using a quantum mechanical embedded cluster approach. We make extensive comparisons with results obtained using Mott-Littleton calculations and data from periodic density functional studies by ourselves and other authors. We show that the embedded cluster method gives reliable energies for a range of defect reactions, including cation vacancy formation, binding between defects, and formation of hydrogen defects by reaction with water. We propose that the embedded cluster techniques should be the method of choice when studying point defects in minerals.