Hypertonic sugar compositions administered by other than ingestion and swallowing or intravascular injection, such as by intranasal spray or drops, intraocular drops or ointment, oral spray, intraotic spray or drops, lozenges, chewable tablet, chewing gum, or gargle, pulmonary inhalation, vaginal or rectal suppositories, or transdermal creams, ointments, lotions, or patches, are effective to open the blood-brain barrier to permit entry into the central nervous system of a co-administered chemical compound, such as a nutrient or a therapeutic or diagnostic agent. In this way, the compositions and methods of the invention increase the therapeutic or diagnostic efficacy of such chemical compounds.