You need to check all labels on medicines, vitamins, supplements etc. to check for binders that may be made from wheat starch. These are areas that may contain hidden gluten "hits" that many people are unaware of. Ask your pharmacist for the ingredients on any prescriptions before you get them filled. They should be able to supply the ingredient list straight from their primary container and verify the medication is gluten free before you fill the prescription in case you need another manufacturer's version. Your pharmacist should also be able to find out which pharmacy carries the manufacturer you need. Don't be afraid to ask questions!
This link is a pretty comprehensive list of gluten free medicines. You can check the resource list at the bottom of the document for additional information.
Gluten Free Drugs.com Is a more recently investigated and updated list of medicines. There is some questionable information on the home page about sugar alcohol that you need to read for yourself and some of the research is taken from a 2007 site at Celiac.com so as always be prepared to make educated decisions for yourself on what your body can and can not handle based on your medical needs.