Thyroid hormone levels linked to ketamine response in bipolar depression, not major depression

The question

Can a simple blood test — baseline thyroid-stimulating hormone (TSH) — help predict who responds to a single intravenous dose of ketamine for hard-to-treat depression?

What they did

Researchers re-analyzed data from four NIH-sponsored randomized, placebo-controlled, double-blind crossover trials of intravenous ketamine (0.5 mg/kg) in hospital inpatients. The group included 39 people with major depressive disorder and 44 with bipolar depression. TSH, a hormone that reflects thyroid activity, was measured before the first infusion of either ketamine or saline placebo, with a two-week gap before the second infusion. Depression, anhedonia (loss of pleasure) and suicidal thoughts were rated at 230 minutes and at days 1, 2 and 7, using statistical models that accounted for thyroid disease, lithium use and how severe the depression was at the start.

What they found

In people with bipolar depression, higher baseline TSH levels were associated with larger drops in depression scores after ketamine compared with placebo (p < 0.0007) and with larger drops in anhedonia (p < 0.0001). In people with major depressive disorder, TSH levels showed no association with changes in depression, anhedonia or suicidal thoughts after ketamine. TSH was not linked to changes in suicidal thinking in either group.

The fine print

This was an exploratory analysis that was not the original purpose of the trials, so the findings need to be confirmed in studies designed to test them. The groups were small (39 with major depression, 44 with bipolar depression), participants were inpatients receiving a single infusion, and follow-up ran only to day 7. The abstract reports p-values but not the size of the effect or the actual TSH ranges involved, and this summary is based on the abstract alone.

What it means

Thyroid hormone levels before treatment may be one clue to who responds to ketamine in bipolar depression, but this is an early exploratory signal, not a test ready for clinical use.

Evidence grade: Low. This is an exploratory secondary analysis of pooled randomized trial data, with modest numbers in each diagnostic group and a biomarker question the original trials were not designed to answer.

This summary is based on the study’s published abstract.