The present invention provides a composition and a method for efficiently delivering a nucleic acid agent to the central nervous system and/or the retina and bringing about antisense effects. Provided is a composition for reducing the expression level of a target transcription product in the central nervous system and/or retina of a subject, the composition including a nucleic acid complex that includes a first nucleic acid strand and a second nucleic acid strand, wherein: the first nucleic acid strand comprises a base sequence capable of hybridizing with at least part of the target transcription product and has an antisense effect on the target transcription product; the second nucleic acid strand comprises a base sequence complementary to the first nucleic acid strand and is conjugated to tocopherol, cholesterol, or an analog thereof; and the first nucleic acid strand is annealed to the second nucleic acid strand.