Coadministration has not been studied. Psyllium husk passes predominantly unchanged through the gastrointestinal tract and there is little opportunity for marked absorption into or metabolism by the body. The mode of action of psyllium husk is physical and does not depend on absorption into the systemic circulation. However, psyllium husk may delay or reduce gastrointestinal absorption of other drugs and it is advisable to separate administration of psyllium husk and orally administered drugs if possible. [Note: this interaction is not specific for emtricitabine and tenofovir-DF, but for any oral medication taken with psyllium husk.]