A composition intended to be employed for therapeutic purposes incorporates an active ingredient (e.g., a source of nicotine) and at a non-active ingredient that is carried by a porous substrate. The non-active ingredient can be a substance that has the capability of affecting the pH of the biological system to which it is applied (e.g., basic substance and/or buffering agent is sorbed onto the porous carrier, so as to be in intimate contact with that carrier). Representative forms of nicotine include free base (e.g., as a mixture of nicotine and microcrystalline cellulose), a nicotine salt (e.g., as nicotine bitartrate) and nicotine polacrilex. The basic substance can be sodium carbonate, and the porous substrate can be microcrystalline cellulose. The composition is useful for treatment of central nervous system conditions, diseases, and disorders, and can be used as a nicotine replacement therapy.