According to DailyMed, Cheratussin AC contains the following INACTIVE ingredients:

- alcohol
- caramel
- citric acid
- FD&C red #40
- flavor
- glycerin
- menthol racemic
- purified water
- saccharin sodium
- sodium benzoate
- sorbitol solution

The manufacturer is Par (now owned by Endo), NDC 0603-1075.

I don't believe any of those ingredients would contain gluten, although I don't know what is contained in their "flavor".

As to other vitamins and medications, one would need to list specifics in order to look up the inactive ingredients and help determine whether there are any gluten-containing compounds.

Update June 13, 2019: I called Par at (800) 828-9393, option 2 - and asked whether Cheratussin contains any gluten. I was told that as of Jan 4 2019, the ingredients are NOT recognized gluten sources ... however they do not test for trace amounts of gluten during the manufacturing process, and their manufacturers are subject to change.

So in other words, the active and inactive ingredients do not contain any gluten ... but they cannot guarantee that trace amounts of gluten don't get into the product during the manufacturing process (i.e. it's not officially certified as gluten free). I suspect they have to say this as a way to protect themselves from liability. If you have an acute gluten sensitivity or Celiac then definitely make your doctor aware before taking this or any other medication.