Gluten free fiber supplements and laxatives are “no problem” for people living gluten free. Metamucil, Fibercon, and Citrucel specify in their frequently-asked-questions sections that they safe for us. Metamucil states that its fiber supplements contain <20 ppm of harmful gluten.
As far as laxatives are concerned, Fleet Laxatives, Phillips, and Senakot specify that their laxatives are gluten free. Phillips reminds us that its laxatives are not manufactured in a dedicated facility.