The desiccant bottle cap includes a cap structure and a desiccant material adhered thereto. The desiccant bottle cap is preferably used to cover a medicine bottle so that the efficiency of the medicine disposed therein will not be impaired by moisture resulting from humid air entering the bottle. In one embodiment, the desiccant bottle cap includes a bottle cap and a desiccant packet affixed to an interior surface thereof. In another embodiment, the desiccant bottle cap includes a bottle cap, a bottle cap liner adhered to an interior surface of the bottle cap, and a desiccant packet adhered to a top surface of the desiccant liner. In yet another embodiment, loose desiccant material or a disk of desiccant material is sandwiched between a bottle cap liner and a porous material to create a bottle cap insert for removable insertion into a bottle cap.