Treating insulin resistance may improve treatment-resistant bipolar depression, early research suggests. In a randomized, placebo-controlled trial, treatment with the diabetes drug metformin reversed insulin resistance in 50% of patients, and this reversal was associated with significant improvement of depressive symptoms. One patient randomly assigned to placebo also achieved a reversal of insulin resistance and improved depressive symptoms.

“The study needs replication, but this early clinical trial suggests that the mitigation of insulin resistance by metformin significantly improves depressive symptoms in a significant percentage of treatment resistant bipolar patients,” presenting author Jessica M. Gannon, MD, University of Pittsburgh Medical Center (UPMC), Pittsburgh, Pennsylvania, told Medscape Medical News.

“It looks like in treatment-resistant bipolar depression treating insulin resistance is a way to get people well again, to get out of their depression,” principal investigator Cynthia Calkin, MD, from Dalhousie University, Halifax, Canada, added.

The findings were presented at the virtual American Society of Clinical Psychopharmacology 2021 Annual Meeting.

Chronic Inflammation

The study was a joint effort by UPMC and Dalhousie University and was sponsored by the Stanley Medical Research Institute.

Patients with bipolar disorder (BD) who are obese tend to have more serious illness, with a more chronic course, more rapid cycling, and more morbidity. These patients also fail to respond to lithium, Calkin said.

“Untreated hyperinsulinemia could be contributing to a state of chronic inflammation and be involved in disease progression. So the question for me was, if we treat this insulin resistance, would patients get better?” she said.

Calkin said investigators used metformin because it is already used by psychiatrists for weight management in patients on antipsychotics.

“I wanted to test the drug that would work to reverse insulin resistance and that psychiatrists would be comfortable prescribing,” she said.

The 26-week study randomly assigned 20 patients to receive metformin and 25 patients to placebo.

All participants were 18 years and older, had a diagnosis of BD I or II, and had nonremitting BD defined by moderate depressive symptoms as measured on the Montgomery-Asberg Depression Rating Scale (MADRS) score of 15 or greater, despite being on optimal, guideline-compatible treatment.

All patients were stable, were on optimal doses of mood-stabilizing medications for at least 4 weeks prior to study entry, and had insulin resistance as defined by a Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) ≥1.8.

 The study was funded by the Stanley Medical Research Institute (SMRI). Calkin and Thase have disclosed no relevant financial relationships.

American Society of Clinical Psychopharmacology (ASCP) 2021: Abstract 3002792 Presented June 2, 2021.