Insulin resistance
November 23, 2005

A recent research study published in the Archives of General Psychiatry supports the view that certain second generation 'antipsychotics,' e.g., Clozaril & Zyprexa, significantly increase resistance to insulin and impair the body's capacity to metabolize glucose even in normal weight patients.

Brian Koehler
New York University

Certain Antipsychotics May Increase Insulin Resistance and Impair Glucose Metabolism

Boston - September 28, 2005—The results of a study led by David C. Henderson, M.D., of Harvard Medical School (2003 Young Investigator), on the relationship between antipsychotic drugs and glucose metabolism, were recently published in Archives of General Psychiatry. Other NARSAD researchers on the team included Eden Evins, M.D. (1996 & 1999 Young Investigator), David B. Allison, Ph.D. (2000 Independent Investigator), and Donald C. Goff, M.D. (2003 Independent Investigator).

Studies have shown that the incidence of diabetes is increasing in schizophrenia patients who are being treated with certain antipsychotic medications. What has been unclear, however, is whether the drugs are affecting the way the body metabolizes glucose, or are simply increasing other risk factors for diabetes – such as weight. Dr. Henderson’s team administered frequent glucose tolerance blood tests to patients taking the two second-generation (also known as atypical) drugs most clearly associated with newly acquired diabetes – clozapine (Clorazil) and olanzapine (Zyprexa) – and compared them with the effects of risperidone (Risperdal).

According to the results of the study, clozapine and olanzapine appear to significantly increase resistance to insulin, as well as impair the body’s ability to metabolize glucose – even in patients of normal weight. Dr. Henderson said of the findings, “In our study comparing the three medications in non-obese patients, we found significant differences between the three drugs on a sensitive measure called the insulin sensitivity index…. both clozapine and olanzapine were associated with significantly reduced insulin sensitivity compared to risperidone.” He went on to say that, “These two drugs appear to be causing insulin resistance, even in non-obese patients, and then there is some sort of impairment in utilization of glucose.” He suggests that patients taking clozapine and olanzapine be examined for insulin resistance and its consequences.