<<Disclaimer: Verify this information before applying it to your situation.>>
I talked to a representative from A.H. Robbins, the manufacturer of
Robitussin, a few months ago. She stated that Robitussin DM is gluten
free. I believe she said that all varieties of Robitussin are GF, but I
am not 100% positive. You might want to check with them if you are
interested in something other than DM. Unfortunately, I can't find the
phone number off hand.
Warren Anderson
Marlborough, MA