A codeine- containing cough syrup lists codeine sulfate as a major ingredient instead of codeine. The Merck

Question:

A codeine- containing cough syrup lists codeine sulfate as a major ingredient instead of codeine. The Merck Index gives C36H44N2O10S as the formula for codeine sulfate. Describe the composition of codeine sulfate. Why is codeine sulfate used instead of codeine?