Background: Impairments in verbal memory and attention are among the most severe and disabling cognitive deficits in patients with schizophrenia. Whereas efficacy for cognition has not yet been established for any pharmacologic strategy in schizophrenia, an accumulating body of evidence suggests a possible beneficial role of insulin.
Methods: We conducted a double-blind, placebo-controlled trial to examine the effect of single-dose intranasal insulin treatment on cognition in nondiabetic patients with schizophrenia. After fasting for 12 hours, subjects received either 40 IU regular human insulin or placebo administered by intranasal pump. The Hopkins Verbal Learning Test and the Continuous Performance Test-Identical Pairs were administered before and 30 minutes after intranasal treatment.
Results: Thirty patients were enrolled and completed the study. The 2 treatment groups (insulin vs placebo, n = 15 in each group) did not differ on any demographic or general clinical variable (P > 0.40). There was no significant difference between the 2 treatment groups in change on Hopkins Verbal Learning Test immediate recall total score and delayed recall score, or on CPT d', hits rate, reaction time of hits, or false-alarm rate (P > 0.1).
Conclusions: Results of the present study suggest that single-dose intranasal insulin treatment does not have a large-enough effect on verbal memory or sustained attention to be detected by a sample of this size in patients with schizophrenia but was safe and well tolerated. Longitudinal studies to explore cognitive benefits of repeated dosing of intranasal insulin treatment are needed.