There is still a little bit of conjecture out there regarding cotton shots. I'm pretty sure that medical science has identified the effects of "Cotton Fever" as being the result of a bacterial infection caused by pantoea agglomerans, which thrive on cotton plants. I'm assuming this is the primary reason for asking? Given that the condition of cotton fever is caused by bacteria, I would recommend boiling, but I am at this point unaware of how or if boiling somehow effects the cotton in a dangerous way, but I do not believe that it does.
In general, the Opioids available on the street are necessarily soluble in water. This means that water and maybe a wringing action of the cotton would be enough to release 90% of your drugs into the solution. Remember, cotton fever is always a possibility. I knew a guy who kept his cottons in the freezer. Once again, given bacteria as the primary actors in this, I wouldn't doubt there to be some utility in such a practice.