Angie, there is a great web site called MedicineNet.com, you can go to and type in what meds you wonte info on and it will bring up side effects and anything else you would like to know on medicins, I hope this is of help too you it does say weight gain and other side effects for decadron, check it out and keep this web site handy to check out any other meds, that your family get that are new, good luck your son, I also have not one but two girls with CAH and I had a son with CAH but he died 14 days after his birth, so I know what your going threw , my girls are now 13 and 5 1/2 so if I can help you any further please let me know I will try my best to answer any questions you may have, Sincerly Brenda